Remove old symbols from QOpenGLContext

Task-number: QTBUG-38564
Change-Id: I39a0482e4411cdc644ed34813626c39dacb5b6af
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>
Fix identical sub-expressions in comparison

Found by static analyzer (see http://www.viva64.com/en/b/0251/).

Change-Id: I611def790a98abf7574e96e6039f10714316d81e
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Jason McDonald <macadder1@gmail.com>