mesa: Don't advertise deprecated extensions in a core context

mesa: Don't advertise deprecated extensions in a core context

It may be possible to trim the list of extensions futher.  These are
just the obvious extensions that add functionality that the core context
explicitly forbids.  Apple's core-context extension list is *just* the
extensions on top of the core GL version.  I'm not sure we want to go
that far, but removing some things that have been in core since 2.1 may
be okay.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>