remove early, unnecessary ESC check

ofAppGLFWWindow has a specific ESC check for app quitting, which didn't respect whether the user had called `ofSetEscapeQuitsApp(false);`. It's an unnecessary check as far as I can tell, since it calls `ofNotifyKeyPressed(key)` right before that, which _does_ perform the check [see here](https://github.com/openframeworks/openFrameworks/blob/master/libs/openFrameworks/events/ofEvents.cpp#L209)

fixes #2549