The linux-f10-* ports will expire on 2017-01-01, remove support for them from Mk/Uses/linux.mk by that time.
While here, simplify the check for 64-bit Linux since only FreeBSD 10.3 and 11.0 will be officially supported by then.
All individual */*f10* ports and games/dsnake (which is linux-f10-only) also have to be removed.