Remove --ash-enable-mirrored-screen flag

Bug: 924322
Test: None
Change-Id: Ief0e8239031f82984c48f08dbf332584f67c5b48
Reviewed-on: https://chromium-review.googlesource.com/c/1428839
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625385}
7 files changed