Revert #18839 as it causes file leaks

```
   > Throwable #1: java.lang.RuntimeException: file handle leaks: [SeekableByteChannel(/var/lib/jenkins/workspace/elastic+elasticsearch+master+g1gc/core/build/testrun/integTest/J0/temp/org.elasticsearch.search.suggest.CompletionSuggestSearch2xIT_518545A20D129C8C-001/tempDir-001/data/nodes/1/indices/4sTECv6WSJOJsw9L4CGamg/0/index/segments_1), SeekableByteChannel(/var/lib/jenkins/workspace/elastic+elasticsearch+master+g1gc/core/build/testrun/integTest/J0/temp/org.elasticsearch.search.suggest.CompletionSuggestSearch2xIT_518545A20D129C8C-001/tempDir-001/data/nodes/1/indices/4sTECv6WSJOJsw9L4CGamg/0/index/segments_1)]
   > 	at __randomizedtesting.SeedInfo.seed([518545A20D129C8C]:0)
   > 	at org.apache.lucene.mockfile.LeakFS.onClose(LeakFS.java:63)
   > 	at org.apache.lucene.mockfile.FilterFileSystem.close(FilterFileSystem.java:77)
   > 	at org.apache.lucene.mockfile.FilterFileSystem.close(FilterFileSystem.java:78)
   > 	at java.lang.Thread.run(Thread.java:745)
   > Caused by: java.lang.Exception
   > 	at org.apache.lucene.mockfile.LeakFS.onOpen(LeakFS.java:46)
   > 	at org.apache.lucene.mockfile.HandleTrackingFS.callOpenHook(HandleTrackingFS.java:81)
   > 	at org.apache.lucene.mockfile.HandleTrackingFS.newByteChannel(HandleTrackingFS.java:271)
   > 	at org.apache.lucene.mockfile.FilterFileSystemProvider.newByteChannel(FilterFileSystemProvider.java:212)
   > 	at org.apache.lucene.mockfile.HandleTrackingFS.newByteChannel(HandleTrackingFS.java:240)
   > 	at java.nio.file.Files.newByteChannel(Files.java:361)
   > 	at java.nio.file.Files.newByteChannel(Files.java:407)
   > 	at org.apache.lucene.store.SimpleFSDirectory.openInput(SimpleFSDirectory.java:77)
   > 	at org.apache.lucene.store.FilterDirectory.openInput(FilterDirectory.java:94)
   > 	at org.apache.lucene.util.LuceneTestCase.slowFileExists(LuceneTestCase.java:2695)
   > 	at org.apache.lucene.store.MockDirectoryWrapper.openInput(MockDirectoryWrapper.java:737)
   > 	at org.apache.lucene.store.FilterDirectory.openInput(FilterDirectory.java:94)
   > 	at org.elasticsearch.common.lucene.Lucene$1.doBody(Lucene.java:237)
   > 	at org.apache.lucene.index.SegmentInfos$FindSegmentsFile.run(SegmentInfos.java:685)
   > 	at org.apache.lucene.index.SegmentInfos$FindSegmentsFile.run(SegmentInfos.java:637)
   > 	at org.elasticsearch.common.lucene.Lucene.checkSegmentInfoIntegrity(Lucene.java:242)
   > 	at org.elasticsearch.index.store.Store$MetadataSnapshot.loadMetadata(Store.java:847)
   > 	at org.elasticsearch.index.store.Store$MetadataSnapshot.<init>(Store.java:740)
   > 	at org.elasticsearch.index.store.Store.getMetadata(Store.java:260)
   > 	at org.elasticsearch.index.store.Store.getMetadata(Store.java:240)
   > 	at org.elasticsearch.index.shard.IndexShard.doCheckIndex(IndexShard.java:1310)
   > 	at org.elasticsearch.common.util.CancellableThreads.executeIO(CancellableThreads.java:102)
   > 	at org.elasticsearch.index.shard.IndexShard.checkIndex(IndexShard.java:1288)
   > 	at org.elasticsearch.index.shard.IndexShard.internalPerformTranslogRecovery(IndexShard.java:921)
   > 	at org.elasticsearch.index.shard.IndexShard.skipTranslogRecovery(IndexShard.java:964)
   > 	at org.elasticsearch.indices.recovery.RecoveryTarget.prepareForTranslogOperations(RecoveryTarget.java:297)
   > 	at
   ```

core/src/main/java/org/elasticsearch/index/shard/IndexShard.java

@@ -53,7 +53,6 @@ import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.util.BigArrays;
 import org.elasticsearch.common.util.Callback;
-import org.elasticsearch.common.util.CancellableThreads;
 import org.elasticsearch.common.util.concurrent.AbstractRunnable;
 import org.elasticsearch.common.util.concurrent.SuspendableRefContainer;
 import org.elasticsearch.index.Index;
@@ -159,7 +158,6 @@ public class IndexShard extends AbstractIndexShardComponent implements IndicesCl
     private final TranslogConfig translogConfig;
     private final IndexEventListener indexEventListener;
     private final QueryCachingPolicy cachingPolicy;
-    private final CancellableThreads cancellableThreads;
 
 
     /**
@@ -267,7 +265,6 @@ public class IndexShard extends AbstractIndexShardComponent implements IndicesCl
         primaryTerm = indexSettings.getIndexMetaData().primaryTerm(shardId.id());
         refreshListeners = buildRefreshListeners();
         persistMetadata(shardRouting, null);
-        cancellableThreads = new CancellableThreads();
     }
 
     public Store store() {
@@ -846,7 +843,6 @@ public class IndexShard extends AbstractIndexShardComponent implements IndicesCl
                 } finally { // playing safe here and close the engine even if the above succeeds - close can be called multiple times
                     IOUtils.close(engine);
                 }
-                cancellableThreads.cancel(reason);
             }
         }
     }
@@ -1285,11 +1281,7 @@ public class IndexShard extends AbstractIndexShardComponent implements IndicesCl
     private void checkIndex() throws IOException {
         if (store.tryIncRef()) {
             try {
-                cancellableThreads.executeIO(this::doCheckIndex);
+                doCheckIndex();
-            } catch (ClosedByInterruptException ex) {
-                assert cancellableThreads.isCancelled();
-                // that's fine we might run into this when we cancel the thread since Java NIO will close the channel on interrupt
-                // and on the next access we fail it.
             } finally {
                 store.decRef();
             }