Revert "app: don't delay FrameEvent.Frame by v-sync latency"

This reverts commit 38ff78df5d, because
it broke OpenGL by moving eglSwapBuffers outside the MakeCurrent
context scope.

Fixes: https://todo.sr.ht/~eliasnaur/gio/393
Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/window.go

@@ -248,7 +248,10 @@ func (w *Window) render(frame *op.Ops, viewport image.Point) error {
 	if err != nil {
 		return err
 	}
-	return w.gpu.Frame(frame, target, viewport)
+	if err := w.gpu.Frame(frame, target, viewport); err != nil {
+		return err
+	}
+	return w.ctx.Present()
 }
 
 func (w *Window) processFrame(d driver, frameStart time.Time) {
@@ -805,9 +808,6 @@ func (w *Window) processEvent(d driver, e event.Event) {
 			// We're done with frame, let the client continue.
 			w.frameAck <- struct{}{}
 		}
-		if err == nil && w.gpu != nil {
-			err = w.ctx.Present()
-		}
 		if err != nil {
 			w.destroyGPU()
 			w.out <- system.DestroyEvent{Err: err}