gl_video: minor simplification

Not needed anymore.
vo_direct3d: check whether D3DFMT_A8 is available

I suspect this is what is happening in github issue #1265 (at least
partially).

If D3DFMT_A8 is not available, fall back to RGBA. This is less efficient
in general, so we normally want to avoid it.
ao_wasapi: don't treat SetDisplayName() failure as fatal

Same for SetIconPath().