webadmin: remove FF10 from optimal-browsers list

As FF10 ESR is approaching its EOL (with the release of FF17 ESR a
couple of months ago), we are removing FF10 from the optimal-browsers
list.

http://www.mozilla.org/en-US/firefox/organizations/faq/
https://wiki.mozilla.org/RapidRelease/Calendar

Change-Id: Icab34a690959fe9c4010ca589af3c6a0d949a776
Bug-Url: https://bugzilla.redhat.com/891877
Signed-off-by: Einav Cohen <ecohen@redhat.com>