yaourt was never removed. It only stopped being included in the new .iso's.
You either changed branches or or got it from upstream or something similar. If you want to get back than just sudo pacman -Syyuu
(this should not be randomly used, but should be used if a package is newer than in repos)
Also to note - You're allowed to have yaourt. It shouldnt break anything. Mixing foreign repos on the other hand could.