The session setvol helper has been removed to reduce the number of
helper functions as the loop over the session's clients isn't very
complicated.

Session mute is handled by setting the master volume to zero.
Signed-off-by: Huw Davies <huw@codeweavers.com>
Signed-off-by: Andrew Eikum <aeikum@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>