The %TailCall runtime entry and the %_TailCall intrinsic is not used,
and will never be used (because %TailCall doesn't actually do a tail
call). We will soon have proper ES6 tail calls, which are correct and
properly tested.

The %Apply runtime entry is basically a super-slow, less correct version
of Reflect.apply, so we can as well just use Reflect.apply, which is
exposed to builtins via %reflect_apply.

R=ishell@chromium.org

Review URL: https://codereview.chromium.org/1739233002

Cr-Commit-Position: refs/heads/master@{#34317}