Bug 12245 - PROG/CCSR deprecation: Remove OPACMobileUserCSS system preference

Bug 12245 - PROG/CCSR deprecation: Remove OPACMobileUserCSS system preference

With CCSR now deprecated there is no longer a need for the
OPACMobileUserCSS system preference. This patch removes it.

To test, apply the patch and run updatedatabase. Check that the
preference can no longer be found in system preferences.

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Preference removed, no koha-qa errors.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>