Remove no existing commits assertion in onInit()

This assertion does not hold if a shard is recovered from an empty store
but failed then retries. Moreover, if the openMode is CREATE_INDEX_*, we
pass CREATE mode to the IndexWriterConfig to create a new index and
overwrite the existing one.

Closes #27960

core/src/main/java/org/elasticsearch/index/engine/CombinedDeletionPolicy.java

@@ -53,7 +53,6 @@ final class CombinedDeletionPolicy extends IndexDeletionPolicy {
     public void onInit(List<? extends IndexCommit> commits) throws IOException {
         switch (openMode) {
             case CREATE_INDEX_AND_TRANSLOG:
-                assert commits.isEmpty() : "index is created, but we have commits";
                 break;
             case OPEN_INDEX_CREATE_TRANSLOG:
                 assert commits.isEmpty() == false : "index is opened, but we have no commits";