[Backport 2.x] Remove FileWatcher from KNN (#2182)

[0ctopus13prime]

Signed-off-by: Dooyong Kim [email protected]

backporting from #2182

[0ctopus13prime]

The last test failed because in Linux, it creates two segments while we are expecting three files will be created in a single segment.
Will update the commit after fixed it to always generate one single segment, so that file name querying will match the number of vector fields.

In testNativeEngineVectorFormat_whenMultipleVectorFieldIndexed_thenSuccess

...

IndexSearcher searcher = new IndexSearcher(indexReader);
final LeafReader leafReader = searcher.getLeafContexts().get(0).reader();
SegmentReader segmentReader = Lucene.segmentReader(leafReader);
final List<String> hnswfiles = getFilesFromSegment(dir, FAISS_ENGINE_FILE_EXT);
assertEquals(3, hnswfiles.size()); <--------- THIS!! Unlike other platform, Linux create two segments.


In Mac, created files in segment 0 : [_0_165_byte_field.faiss, _0_165_float_binary_field.faiss, _0_165_float_field.faiss]
In Linux, two segments were created (e.g. 0 + 1) : [_0_165_byte_field.faiss, _0_165_float_binary_field.faiss, _0_165_float_field.faiss, _1_165_float_binary_field]

Therefore, the test is not failing because of the change. Will fix the test.