Those two methods are spread over the code base, and their purpose is
often not clear. Historically, they were used to turn pointers into
integers in order to do computations on them. Today we have {Address}
which is uintptr_t, so we can compute directly on that.

This also makes the {RoundUp} and {RoundDown} macros only work on
integral values (including {Address}).

R=mlippautz@chromium.org

Bug: v8:8015
Change-Id: Ia98fb826793ee5d3a2a5b18c09c329d088443772
Reviewed-on: https://chromium-review.googlesource.com/1233914Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56048}