vo_vaapi: don't redraw twice

After VOCTRL_REDRAW_FRAME, flip_page is called, which renders the frame.
The current code rendered the frame twice; drop the redundant call.
vo: remove config_ok check from vo_check_events()

This should be ok now after the x11 code was adjusted.
vo: minor simplifications
build: "tv-v4l2" needs "tv"

Fixes #795.
x11: fix a warning with --disable-xext

Signed-off-by: wm4 <wm4@nowhere>