Delete unused support for @hidden JSDoc tag & JSMessage.isHidden()

PiperOrigin-RevId: 698056995

Author: lauraharker

src/com/google/javascript/jscomp/serialization/JSDocSerializer.java

@@ -322,6 +322,11 @@ private static JSTypeExpression createPlaceholderType() {
           builder.recordAbstract();
           continue;
 
+        case JSDOC_HIDDEN:
+          // TODO(b/238215455): delete this case once the change to stop
+          // serializing hidden JSDoc tags lands in a release.
+          continue;
+
           // TODO(lharker): stage 2 passes ideally shouldn't report diagnostics, so this could be
           // moved to stage 1.
         case JSDOC_SUPPRESS_MESSAGE_CONVENTION:

src/com/google/javascript/rhino/typed_ast/optimization_jsdoc.proto

@@ -48,6 +48,7 @@ enum JsdocTag {
   JSDOC_ABSTRACT = 19;
 
   // Used by ReplaceMessage i18n
+  JSDOC_HIDDEN = 21;
   JSDOC_SUPPRESS_MESSAGE_CONVENTION = 22;
 
   // Used by CollapseProperties