glx: Remove GLX_USE_APPLEGL cruft in extension string handling

glx: Remove GLX_USE_APPLEGL cruft in extension string handling

All of the extensions require that both libGL and either the server or
the direct rendering driver (or both) enable the extension before it's
advertised.  It seems safe to assume that none of the other components
on OS X will enable these extensions, so all the #ifdef blocks here
just clutter the code.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Cc: Jeremy Huddleston <jeremyhu@apple.com>