Restoring your backup unfortunately won't let you run the Ruu. The update upgraded your hboot which won't change back from restoring a backup. Probably the closest you could get at this point would be to flash a fresh copy of the stock rom and relock they bootloader. Though, the average user wouldn't even know it's unlocked. And anyone that cared would probably be happy to find it already done for them. Plus you will get the RELOCKED SECURITY WARNING on the bootloader which looks worse than unlocked Imo.