[autotest] Remove obsolete 'mirror' code.

This code has no callers in the source.  On cautotest, the code has
not been invoked (no .pyc files).  Moreover, inspection indicates
the code serves no purpose for the Chrome OS lab.  So, let's bury
the body before it gets any moldier.

BUG=None
TEST=None

Change-Id: Ib0ba025178cf02bb63128619728e123b8a3eafe6
Reviewed-on: https://chromium-review.googlesource.com/265353
Tested-by: Richard Barnette <jrbarnette@chromium.org>
Reviewed-by: Fang Deng <fdeng@chromium.org>
Commit-Queue: Richard Barnette <jrbarnette@chromium.org>
10 files changed