Don't bother using %_IsJSReceiver, which immediately gets lowered to
ObjectIsReceiver anyways (by the JSIntrinsicLowering), but requires
some complicated rewiring of effect/control chains.

R=mstarzinger@chromium.org
BUG=chromium:640369

Review-Url: https://codereview.chromium.org/2271973003
Cr-Commit-Position: refs/heads/master@{#38864}