Immediate::is_zero already checks the reloc info to be none, so the
additional check is redundant.

R=tebbi@chromium.org

Change-Id: I3ec91fe60e8c659b2f38fda0123784a69e4bcbe9
Reviewed-on: https://chromium-review.googlesource.com/878321Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50760}