Restore all aliases and delete unused variables.

def pop_scope(self, aliases, frame):
        """Restore all aliases and delete unused variables."""
        for name, alias in aliases.iteritems():
            self.writeline('l_%s = %s' % (name, alias))
        to_delete = set()
        for name in frame.identifiers.declared_locally:
            if name not in aliases:
                to_delete.add('l_' + name)
        if to_delete:
            # we cannot use the del statement here because enclosed
            # scopes can trigger a SyntaxError:
            #   a = 42; b = lambda: a; del a
            self.writeline(' = '.join(to_delete) + ' = missing')