Delete unnecessary flush in Lucene90CompressingStoredFieldsWriter.copyChunks() to reduce dirty chunks

else if (matchingFieldsReader.getCompressionMode() == compressionMode && 
                 matchingFieldsReader.getChunkSize() == chunkSize && 
                 matchingFieldsReader.getPackedIntsVersion() ==PackedInts.VERSION_CURRENT &&
                 liveDocs == null &&
                 !tooDirty(matchingFieldsReader)) { 
       ......
       // flush any pending chunks
        if (numBufferedDocs > 0) {
          flush();
          numDirtyChunks++; // incomplete: we had to force this flush
        }
       ......
}