Remove custom KnnVectorFieldExistsQuery (#85945)

This query was added to Lucene in version 9.1, so we can delete our version in
favor of using the Lucene one.

Author: jtibshirani

x-pack/plugin/vectors/src/main/java/org/elasticsearch/xpack/vectors/mapper/DenseVectorFieldMapper.java

@@ -14,6 +14,7 @@
 import org.apache.lucene.document.KnnVectorField;
 import org.apache.lucene.index.VectorSimilarityFunction;
 import org.apache.lucene.search.DocValuesFieldExistsQuery;
+import org.apache.lucene.search.KnnVectorFieldExistsQuery;
 import org.apache.lucene.search.KnnVectorQuery;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.util.BytesRef;
@@ -39,7 +40,6 @@
 import org.elasticsearch.xcontent.ToXContent;
 import org.elasticsearch.xcontent.XContentBuilder;
 import org.elasticsearch.xcontent.XContentParser.Token;
-import org.elasticsearch.xpack.vectors.query.KnnVectorFieldExistsQuery;
 import org.elasticsearch.xpack.vectors.query.VectorIndexFieldData;
 
 import java.io.IOException;

x-pack/plugin/vectors/src/main/java/org/elasticsearch/xpack/vectors/query/KnnVectorFieldExistsQuery.java

@@ -16,6 +16,7 @@
 import org.apache.lucene.document.KnnVectorField;
 import org.apache.lucene.index.IndexableField;
 import org.apache.lucene.search.DocValuesFieldExistsQuery;
+import org.apache.lucene.search.KnnVectorFieldExistsQuery;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.Version;
@@ -33,7 +34,6 @@
 import org.elasticsearch.xpack.vectors.DenseVectorPlugin;
 import org.elasticsearch.xpack.vectors.mapper.DenseVectorFieldMapper.DenseVectorFieldType;
 import org.elasticsearch.xpack.vectors.mapper.DenseVectorFieldMapper.VectorSimilarity;
-import org.elasticsearch.xpack.vectors.query.KnnVectorFieldExistsQuery;
 
 import java.io.IOException;
 import java.nio.ByteBuffer;