vo_gl2, vo_matrixview: remove these VOs

vo_gl2, vo_matrixview: remove these VOs

Delete the vo_gl2 and vo_matrixview implementations.

vo_gl2 was barely useful anymore. It was a hack based on an old
vo_gl.c version, and all it did differently was rendering the video in
tiles instead of using a single texture. That made it work with some
crappy OpenGL implementations. These days all GPUs support textures of
at least 2048x2048 pixels, which is enough for HD playback. On the
other hand, gl2 suffered from various bugs and deficiencies, all of
which are fixed in gl. Its existence also confused users; many thought
that gl2 is the next version of gl and attempted to use it, even
though it's much worse than gl and they should have used that instead.

Should it turn out that tiling is actually useful, it should be
implemented in vo_gl, instead of keeping vo_gl2 alive.

vo_matrixview was a toy that couldn't even properly display a video.
All it did was display a screensaver-like animation that showed "a
Matrix-like running-text effect". (mplayer is not a screensaver.)