Make TransportClusterStateAction abide to our style (#30697)

I still do not like == false. However, I am so use to reading it that
today I read this line of code and could not understand how it could
possibly be doing the right thing. It was only when I finally noticed
the ! that the code made sense. This commit changes this code to be in
our style of == false. I still do not like == false.

server/src/main/java/org/elasticsearch/action/admin/cluster/state/TransportClusterStateAction.java

@@ -115,9 +115,9 @@ protected void masterOperation(final ClusterStateRequest request, final ClusterS
                 mdBuilder = MetaData.builder(currentState.metaData());
             }
 
-            // Filter our metadata that shouldn't be returned by API
-            for(ObjectObjectCursor<String, Custom> custom : currentState.metaData().customs()) {
-                if(!custom.value.context().contains(MetaData.XContentContext.API)) {
+            // filter out metadata that shouldn't be returned by the API
+            for (ObjectObjectCursor<String, Custom> custom : currentState.metaData().customs()) {
+                if (custom.value.context().contains(MetaData.XContentContext.API) == false) {
                     mdBuilder.removeCustom(custom.key);
                 }
             }