[TEST] remove feature yaml from REST tests

The only runner that supported it was the java runner, we can use json format instead given that the default one with cat apis is text

rest-api-spec/src/main/resources/rest-api-spec/test/cat.aliases/30_yaml.yaml

@@ -1,8 +1,5 @@
 ---
-"Simple alias with yaml body through format argument":
-
-  - skip:
-      features: yaml
+"Simple alias with json body through format argument":
 
   - do:
         indices.create:
@@ -15,7 +12,7 @@
 
   - do:
       cat.aliases:
-        format: yaml
+        format: json
 
   - match: {0.alias: test_alias}
   - match: {0.index: test}

test/framework/src/main/java/org/elasticsearch/test/rest/support/Features.java

@@ -34,7 +34,7 @@ import java.util.List;
  */
 public final class Features {
 
-    private static final List<String> SUPPORTED = Arrays.asList("stash_in_path", "groovy_scripting", "headers", "yaml");
+    private static final List<String> SUPPORTED = Arrays.asList("stash_in_path", "groovy_scripting", "headers");
 
     private Features() {