Unskip JSAtomicsMutexTest.Contention test

The test should now be self-skipping without extra work

Bug: v8:12547
Change-Id: I0adf5d8745e19b17d2644587e416eb16063b210d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3694455Reviewed-by: Milad Farazmand <mfarazma@redhat.com>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81013}

test/unittests/unittests.status

@@ -73,12 +73,6 @@
   'SweeperTest.DiscardingNormalPageMemory': [SKIP],
 }],  # arch == ppc64
 
-##############################################################################
-['no_js_shared_memory', {
-  # Tests that require shared cage implemented.
-  'JSAtomicsMutexTest.Contention': [SKIP],
-}],  # no_js_shared_memory
-
 ##############################################################################
 ['system == windows and asan', {
   # BUG(893437).