Remove JavaScript const/let/lambda presubmit check for iOS9.

iOS9 is not supported by Chrome iOS and iGSA anymore, the presubmit check
for risky ES6 grammar(const/let/lambda) can be removed now.

Change-Id: I5a35d54097dbd215393aaba78868107befdc93b6
Reviewed-on: https://chromium-review.googlesource.com/c/1329249
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Yi Su <mrsuyi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606867}
2 files changed