Rename ClusterState#lookupPrototypeSafe to lookupPrototype and remove previous "unsafe" unused variant (#21686)

The `lookupPrototype` method is not used anywhere. Seems like we rather use its `lookupProrotypeSafe` variant (which also throws exception if the prototype is not found) is always. This commit makes the safer variant the default one, by renaming it to  "lookupPrototype" and removes the previous "unsafe" variant.

Author: javanna

core/src/main/java/org/elasticsearch/cluster/ClusterState.java

@@ -108,13 +108,7 @@ public static void registerPrototype(String type, Custom proto) {
         registerPrototype(RestoreInProgress.TYPE, RestoreInProgress.PROTO);
     }
 
-    @Nullable
     public static <T extends Custom> T lookupPrototype(String type) {
-        //noinspection unchecked
-        return (T) customPrototypes.get(type);
-    }
-
-    public static <T extends Custom> T lookupPrototypeSafe(String type) {
         @SuppressWarnings("unchecked")
         T proto = (T) customPrototypes.get(type);
         if (proto == null) {
@@ -308,7 +302,7 @@ public enum Metric {
 
         private final String value;
 
-        private Metric(String value) {
+        Metric(String value) {
             this.value = value;
         }
 
@@ -630,10 +624,6 @@ public Builder stateUUID(String uuid) {
             return this;
         }
 
-        public Custom getCustom(String type) {
-            return customs.get(type);
-        }
-
         public Builder putCustom(String type, Custom custom) {
             customs.put(type, custom);
             return this;
@@ -707,7 +697,7 @@ public ClusterState readFrom(StreamInput in, DiscoveryNode localNode) throws IOE
         int customSize = in.readVInt();
         for (int i = 0; i < customSize; i++) {
             String type = in.readString();
-            Custom customIndexMetaData = lookupPrototypeSafe(type).readFrom(in);
+            Custom customIndexMetaData = lookupPrototype(type).readFrom(in);
             builder.putCustom(type, customIndexMetaData);
         }
         return builder.build();
@@ -779,12 +769,12 @@ public ClusterStateDiff(StreamInput in, ClusterState proto) throws IOException {
                 new DiffableUtils.DiffableValueSerializer<String, Custom>() {
                     @Override
                     public Custom read(StreamInput in, String key) throws IOException {
-                        return lookupPrototypeSafe(key).readFrom(in);
+                        return lookupPrototype(key).readFrom(in);
                     }
 
                     @Override
                     public Diff<Custom> readDiff(StreamInput in, String key) throws IOException {
-                        return lookupPrototypeSafe(key).readDiffFrom(in);
+                        return lookupPrototype(key).readDiffFrom(in);
                     }
                 });
         }