(now rebased on top of ther other MR that pushed the mesa/ subset)
A minor distraction from the format enums, themselves, let's delete more hand-written, GL format/type <-> MESA_FORMAT code from st/.
@kwg who was just in st_formats.c and might be able to push this to intel ci for me. This doesn't clean up what we were looking at in st_formats.c, though I have thoughts about doing so in general.