This removes the obsolete {Crankshaft} factory method as it returns the
same configuration as the {Turbofan} factory by now. We now consistently
use {RegisterConfiguration::Default} everywhere.

R=jkummerow@chromium.org
BUG=v8:6408

Change-Id: I6be25774aa6714ef4dc1ef6856bb6dbc95593a29
Reviewed-on: https://chromium-review.googlesource.com/597858Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47109}