mesa: Remove all vestiges of glFramebufferTextureFaceARB

mesa: Remove all vestiges of glFramebufferTextureFaceARB

Mesa does not (and probably never will) support GL_ARB_geometry_shader4,
so this function will never exist.  Having a function that is
exec="skip" and offset="assign" is just weird.

There are still a couple 'exec="skip" offset="assign"' functions
remaining.  These remain because we either support GLX protocol for them
(glSampleMaskSGIS and glSamplePatternSGIS) or older DRI drivers still
need them in the dispatch table (glResizeBuffersMESA).  The SGIS
functions can be removed later.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>