Remove obsolete functionality from the MacroAssemblers.

Remove obsolete functionality from the MacroAssemblers.

This is uncontroversial the dead code removal part of
https://codereview.chromium.org/1307943013, which was
previously landed, but got reverted because of DOM
breakage that requires more investigation.

TBR=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/1322843005

Cr-Commit-Position: refs/heads/master@{#30577}