The internal index used to implement for-in can never leave the
valid smi range, so there's no need to actually check for overflow
in Crankshaft. In fact the overflow only triggered a false alert
in the deopt fuzzer.

R=jarin@chromium.org
BUG=v8:3650
LOG=n

Review URL: https://codereview.chromium.org/1621623002

Cr-Commit-Position: refs/heads/master@{#33456}