intel/compiler: Don't allocate memory for SIMD select error handling

The position in the error array already indicate the SIMD in question,
so take off all the formatted printing from the errors -- which in some
cases were just not needed.  We lose a little bit of extra context but
it is all easily derivable from the message and the SIMD.

This also will remove the overhead when SIMD selection is being used to
just to find the selected dispatch width -- at a point where the shaders
were already compiled -- and the errors are not used at all.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/9849
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25336>

src/intel/compiler/test_simd_selection.cpp

@@ -46,7 +46,6 @@ protected:
    , devinfo(rzalloc(mem_ctx, intel_device_info))
    , prog_data(rzalloc(mem_ctx, struct brw_cs_prog_data))
    , simd_state{
-      .mem_ctx = mem_ctx,
       .devinfo = devinfo,
       .prog_data = prog_data,
      }