Unset
From Scriptwiki
Unsets and removes a variable from the variable list.
/unset [-s] <%var>
The -s switch gives an output: * Unset %var
Note that you can specify a variable with wildcard characters.
Example
/unset %moo
This will unset and remove the variable %moo.
/unset %test*
This will unset and remove all variables that begin with %test.