[Test] Remove dead code from ExceptionSerializationTests (#34713)

The `ignore` set contains entries of type Class<?>, but the check is performed
on Path objects. This always returns false so is useless currently. Looking at
the first commit of this test that already shows this behaviour this never
excluded anything, so it can be removed.

server/src/test/java/org/elasticsearch/ExceptionSerializationTests.java

@@ -133,11 +133,7 @@ public class ExceptionSerializationTests extends ESTestCase {
 
             @Override
             public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
-                Path next = pkgPrefix.resolve(dir.getFileName());
-                if (ignore.contains(next)) {
-                    return FileVisitResult.SKIP_SUBTREE;
-                }
-                pkgPrefix = next;
+                pkgPrefix = pkgPrefix.resolve(dir.getFileName());
                 return FileVisitResult.CONTINUE;
             }