Remove display-options-display-view-mirroring.

Remove display-options-display-view-mirroring.

In the CSS, this name is used for an ID, but in the JS side
this name is used for a class name, it seems this name is just
unused.

It would be okay to use this as a class name, but this specifies
margin only, and we don't see any claims about margin for mirroring
view. Actually, mirroring displays are centered and sized well,
so nobody notices the margin for the container. Let's just remove
unused code.

BUG=None
R=dbeam@chromium.org

Committed: https://crrev.com/8cc7fae05c3dc2c85bfce2348a12ad913e677ba2
Cr-Commit-Position: refs/heads/master@{#318534}

[Dan Beam, 2015-02-27 21:29:06]

lgtm++

[Jun Mukai, 2015-02-27 21:30:01]

The CQ bit was checked by mukai@chromium.org

[commit-bot: I haz the power, 2015-02-27 21:32:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/967623002/1

[commit-bot: I haz the power, 2015-02-27 22:39:15]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-27 22:40:04]

Patchset 1 (id:??) landed as
https://crrev.com/8cc7fae05c3dc2c85bfce2348a12ad913e677ba2
Cr-Commit-Position: refs/heads/master@{#318534}