[NFC][AMDGPU] don't test asyncmark for non-async variants on pre-gfx12
The test for asyncmark on pref-gfx12 targets, checks the effect of async marks
on both async and non-async instructions. This is achieved by a sed invocation
in the RUN line to remove the .async from intrinsic name.
Such a test serves no purpose other than a minor flex. The two sets of CHECK
lines using the WITH and WITHOUT prefix are not easy to compare by a simple
eyeballing. Eliminating this hack makes it easier to add GISEL variants later.
With and without GISEL, the combinations will increase to four instead of the
current two.
Assisted-By: Claude Opus 4.6