Silencing bash's unalias when there's nothing to unalias
Solution 1:
Just redirect the output.
unalias rm mv cp >/dev/null 2>/dev/null
Solution 2:
In bash you could do the following to unalias an alias only if it exists, for example rm:
[ -n "`alias -p | grep '^alias rm='`" ] && unalias rm
Another idea would be to overwrite the alias, even it if exists:
alias rm='/bin/rm'