Also updates TurboAssembler::DropArguments to simplify dropping the receiver
and the arguments.

Bug: v8:6644
Change-Id: Ief3b529ffc574c213816a533948c7b1f5d014bd7
Reviewed-on: https://chromium-review.googlesource.com/723466Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Georgia Kouveli <georgia.kouveli@arm.com>
Cr-Commit-Position: refs/heads/master@{#48669}