This just removes some left-overs from when the {JSTypedLoweringTest}
covered strong mode and an iteration over all language modes was used
for testing all binary operations. The language mode in question has
been removed since then.

R=bmeurer@chromium.org

Review-Url: https://codereview.chromium.org/2121113002
Cr-Commit-Position: refs/heads/master@{#37526}