I mostly use yaourt instead of pacman to make my life easier when installing AUR packages. But they have the same syntax for this specific task.

Remove a package along with its installed dependencies

$ yaourt -Rcs <package>
  • R remove
  • c clean all these (.pacnew, .pacsave and .pacorig) files
  • s Remove each target specified including all of their dependencies, provided that (A) they are not required by other packages; and (B) they were not explicitly installed by the user.