perf test pmu: Remove unused test_pmus

perf test pmu: Remove unused test_pmus

Commit aa1551f299ba ("perf test pmu: Refactor format test and exposed
test APIs") added the 'test_pmus' list, but didn't use it.
(It seems to put them on the other_pmus list?)

Remove it.

Fixes: aa1551f299ba414c ("perf test pmu: Refactor format test and exposed test APIs")
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Link: https://lore.kernel.org/lkml/20240727175919.1041468-1-linux@treblig.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>