LibJS: Remove MarkedValueList in favor of MarkedVector<Value> :^)

Author: https://github.com/linusg
Commit: 7676b1b925
Pull-request: https://github.com/SerenityOS/serenity/pull/12376
Reviewed-by: https://github.com/IdanHo

Userland/Libraries/LibJS/Forward.h

@@ -159,7 +159,6 @@ class HandleImpl;
 class Heap;
 class HeapBlock;
 class Interpreter;
-class MarkedValueList;
 class Module;
 class NativeFunction;
 class ObjectEnvironment;