Remove the exclusive FFP mode

!4771 (merged)

This is required to eventually move on to the OpenGL core profile which would improve rendering functionality under video drivers where OpenGL 2.1 is implemented poorly.

This will also make implementing certain visual features easier as we wouldn't have to keep FFP at least somewhat in mind, even if to ignore it.

This will also simplify the renderer considerably.

This will also make it impossible to directly compare the rendering state with the original game's FFP state but who cares :todd: (#8993).

etc. etc. etc. the benefits outweigh the negatives.

...

It's over 9000!