Remove non-existent object-observe test from mjsunit.status

TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/1907423002 .

Cr-Commit-Position: refs/heads/master@{#35740}

test/mjsunit/mjsunit.status

@@ -259,7 +259,6 @@
   # Slow tests.
   'copy-on-write-assert': [PASS, SLOW],
   'debug-scopes': [PASS, SLOW],
-  'es7/object-observe': [PASS, ['mode == debug', SLOW]],
   'numops-fuzz-part*': [PASS, ['mode == debug', SLOW]],
   'readonly': [PASS, SLOW],
   'regress/regress-1200351': [PASS, ['mode == debug', SLOW]],