Remove unused methods in sun.misc.JavaAWTAccess

The following methods in sun.misc.JavaAWTAccess are no longer needed and should be removed:
    public Object get(Object key);
    public void put(Object key, Object value);
    public void remove(Object key);
    public boolean isDisposed();
    public boolean isMainAppContext();

The only dependency from core-libs to AppContext is the ability to determine if it is running in an applet environment and obtain an opaque unique object to represent different applet context.

we should be cautious in adding back any dependency to AppContext in the future.