[wasm] Enable wasm imported memory tests on gc_stress

Issues with instance wrapper allocation and JS Api errata have been fixed over the last few weeks, test in the bug no longer fails - enabling tests for imported memory.

BUG=5683

R=bradnelson@chromium.org, ahaas@chromium.org

Review-Url: https://codereview.chromium.org/2666763002
Cr-Commit-Position: refs/heads/master@{#42795}

test/mjsunit/mjsunit.status

@@ -240,10 +240,6 @@
 
   # BUG(v8:4779): Crashes flakily with stress mode on arm64.
   'array-splice': [PASS, SLOW, ['arch == arm64', FAST_VARIANTS]],
-
-  #BUG(v8:5683)
-  'wasm/import-memory': [SKIP],
-
 }],  # 'gc_stress == True'
 
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