tt(DELETENOUSERMACRO) removes a `nousermacro' definition. The
function expects one argument: the name of the `nousermacro' identifier to be
removed from the nousermacro-set.

There is no error condition (except for syntax errors): when the identifier
wasn't stored as a `nousermacro' no action is taken.

    Example:
        verb(\
    DELETENOUSERMACRO(mymacro)
        )

