gallium/xlib: remove GL_{MAJOR,MINOR,TINY}

gallium/xlib: remove GL_{MAJOR,MINOR,TINY}

These variables were removed from autotools in 2008 (sha:
80f68e1b6a0e5bd2da799c), but they have lived on here. The Scons build
meanwhile doesn't set a patch/tiny version at all, just major and minor.
This patch removes the unused variables and simply sets the version,
leaving patch/tiny as 0 since that's what the autotools build as been
doing forever. This shouldn't change any behavior.

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Brian Paul <brianp@vmware.com>