egl/glx: Remove egl_glx driver

Mesa now has a real, feature-rich EGL implementation on X11 via xcb.
Therefore I believe there is no longer a practical need for the egl_glx
driver.

Furthermore, egl_glx appears to be unmaintained.  The most recent
nontrivial commit driver was 6baa5f1 on 2011-11-25.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>