GLSL-to-TGSI going away

I just posted a status update to the MR with the summary of remaining work:

https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8044#note_1346175

I started this project back in December 2020, and have been pushing all the
TGSI drivers along since then.  We're down to very few test regressions in
the remaining drivers, and landing it nets us test fixes and performance
wins while removing 22,000 lines of unmaintained, non-CI-tested code.

This email is your warning that, once those linked MRs land, I plan on
landing !8044 and saying goodbye to the GLSL-to-TGSI path.