Remove xpack actions for vector field

We have already decided not to have xpack usage for field mappers
(see elastic#53076). As mappings stats of all fields is already tracked
in cluster stats.
Moreover xpack usage for vector field is a quite expensive operation
(see elastic#74974).

This removes xpack actions for vector field.

Backport for elastic#75017

docs/reference/rest-api/info.asciidoc

@@ -146,10 +146,6 @@ Example response:
          "available" : true,
          "enabled" : true
       },
-      "vectors" : {
-         "available" : true,
-         "enabled" : true
-      },
       "voting_only" : {
          "available" : true,
          "enabled" : true

docs/reference/rest-api/usage.asciidoc

@@ -276,13 +276,6 @@ GET /_xpack/usage
     "available" : true,
     "enabled" : true
   },
-  "vectors" : {
-    "available" : true,
-    "enabled" : true,
-    "dense_vector_fields_count" : 0,
-    "dense_vector_dims_avg_count" : 0,
-    "sparse_vector_fields_count" : 0
-  },
   "voting_only" : {
     "available" : true,
     "enabled" : true

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/XPackField.java

@@ -44,6 +44,7 @@ public final class XPackField {
     public static final String TRANSFORM = "transform";
     /** Name constant for flattened fields. */
     public static final String FLATTENED = "flattened";
+    @Deprecated
     /** Name constant for the vectors feature. */
     public static final String VECTORS = "vectors";
     /** Name constant for the voting-only-node feature. */

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/vectors/VectorsFeatureSetUsage.java

@@ -17,6 +17,11 @@
 import java.io.IOException;
 import java.util.Objects;
 
+/**
+ * @deprecated This class exists for backwards compatibility with 7.14 only
+ * and should not be used for other purposes.
+ */
+@Deprecated
 public class VectorsFeatureSetUsage extends XPackFeatureSet.Usage {
 
     private final int numDenseVectorFields;

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

@@ -11,7 +11,6 @@
 import org.elasticsearch.index.mapper.Mapper;
 import org.elasticsearch.plugins.MapperPlugin;
 import org.elasticsearch.plugins.Plugin;
-import org.elasticsearch.xpack.core.XPackPlugin;
 import org.elasticsearch.xpack.vectors.mapper.DenseVectorFieldMapper;
 import org.elasticsearch.xpack.vectors.mapper.SparseVectorFieldMapper;
 
@@ -27,9 +26,7 @@ public class Vectors extends Plugin implements MapperPlugin {
     public Vectors() { }
 
     public Collection<Module> createGuiceModules() {
-        return Collections.singletonList(b -> {
-            XPackPlugin.bindFeatureSet(b, VectorsFeatureSet.class);
-        });
+        return Collections.emptyList();
     }
 
     @Override