mesa: Replace _mesa_pack_ubyte_rgba_row() with pack_ubyte_rgba_8unorm().

mesa: Replace _mesa_pack_ubyte_rgba_row() with pack_ubyte_rgba_8unorm().

The major thing that the codegen had was support for expanding integers
from byte-per-channel to the target format's channel size.  However, the
format_utils.c caller never did that for integers, and swrast doesn't have
support for integers, so that appears to be dead code.  With this done,
format_pack.py goes away entirely.

I slightly changed the prototype of _mesa_pack_ubyte_rgba_row() to match
up with the new function, which involved (mostly) dropping some manual
casts from the callers to make their data match the old prototype.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10336>