The runtime flag in question makes no sense, because the feature cannot
be disabled without keeping the snapshot in sync. We should avoid having
the flag in our "mjsunit" test suite, so that CluserFuzz doesn't pick it
up. The test in question is already skipped, the change will not affect
test results on our waterfall.

R=mvstanton@chromium.org
TEST=mjsunit/call-counts
BUG=v8:4458
LOG=n

Review URL: https://codereview.chromium.org/1409533003

Cr-Commit-Position: refs/heads/master@{#31302}