[rbp] Remove unnecessary gl ifdef

I'm not sure why this was originally added.
I couldn't think of a reason why the Pi would want things done differently here,
so I tried without the ifdef. I can't see any difference in behaviour,
so I think we're better off removing it.
Merge pull request #2686 from popcornmix/remove_gl_ifdef

[rbp] Remove unnecessary gl ifdef
VideoRenerers: add buffering
add buffering for GLES
WinRenderer: add buffering
DXVA: activate buffering in renderer
linuxrenderer: delete all textures on reconfigure
drop frame counter in application, ask render manager instead
vaapi: adopt to buffering in renderer
add buffering - some documentation
move NUM_BUFFERS up to BaseRenderer.h
OverlayRenderer: align buffers with index in renderManager
add buffering - submit absolute time to render buffers
RenderManager: some rework to buffering
dvdplayer: disable buffering unil dropping is improved
RenderManager: skip very late frames in render buffer
renderbuffers: drop enable/disable in this iteration
RenderManager: add method SetSpeed
RenderManager: return bufferlevel with WaitForBuffer
RenderManager: do not drop in renderbuffers, this ruins detection of displayed frame