Remove --ash-force-mirror-mode

BUG=340466

Review URL: https://codereview.chromium.org/182643002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253799 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253799
Cleanup remoting.gyp around the remoting_webapp target

Added two new targets remoting_webapp_v1 and remoting_webapp_v2. Both
include the new remoting_webapp.gypi. remoting_webapp target
depends on both. Also moved these targets to remoting_client.gypi.
remoting_webapp.gypi will also be reused for webapp version that
uses PNaCl plugin.

BUG=276739

Review URL: https://codereview.chromium.org/181473008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253800 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253800