Remove RegExp.prototype.source getter compat workaround

src/js/regexp.js

Index: src/js/regexp.js
diff --git a/src/js/regexp.js b/src/js/regexp.js
index a1055b3dd5e2f876dbe253dab400d53e96ee1aad..43565103f3a9099080dc5b6a2ab3836a70438111 100644
--- a/src/js/regexp.js
+++ b/src/js/regexp.js
@@ -1071,11 +1071,6 @@ function RegExpGetMultiline() {
 // ES6 21.2.5.10.
 function RegExpGetSource() {
   if (!IS_REGEXP(this)) {
-    // TODO(littledan): Remove this RegExp compat workaround
-    if (this === GlobalRegExpPrototype) {
-      %IncrementUseCounter(kRegExpPrototypeSourceGetter);
-      return UNDEFINED;
-    }
     throw MakeTypeError(kRegExpNonRegExp, "RegExp.prototype.source");
   }
   return REGEXP_SOURCE(this);