Revert "[test] Skip tests failing on gc fuzzer"

This reverts commit 4dcf68e9.

Reason for revert: Bug should be fixed.

Original change's description:
> [test] Skip tests failing on gc fuzzer
> 
> Temporarily skipping tests until a fix has landed.
> 
> TBR=ofrobots@google.com
> NOTRY=true
> 
> Bug: v8:7313
> Change-Id: I9d55f1ba190ee8104b90fd80c4b1de05508475e5
> Reviewed-on: https://chromium-review.googlesource.com/888642
> Commit-Queue: Michael Achenbach <machenbach@chromium.org>
> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50900}

TBR=machenbach@chromium.org,ofrobots@google.com,majeski@google.com

Change-Id: I9ac4800331f572e23c24d936f8b6c51884beeacb
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7313
Reviewed-on: https://chromium-review.googlesource.com/888563Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50912}

test/mjsunit/mjsunit.status

@@ -647,12 +647,6 @@
 
   # Fails allocation on tsan.
   'es6/classes': [PASS, ['tsan', SKIP]],
-
-  # BUG(v8:7313).
-  'regress/regress-crbug-474297': [SKIP],
-  'regress/regress-crbug-491062': [SKIP],
-  'regress/regress-crbug-505007-1': [SKIP],
-  'regress/regress-crbug-506443': [SKIP],
 }],  # 'gc_fuzzer'
 
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