staging: line6: drop tuner_pitch sysfs attr

Dropping this final tuner sysfs attr also leaves the
POD_GET_SYSTEM_PARAM() macro, pod_get_system_param_string(), and
pod_get_system_param_int() unused.  Remove them immediately to avoid
compiler warnings.

POD_monitor_level is now the only SYSEX value that needs to be watched
by the driver since the ALSA volume control should reflect the current
monitor volume level used by the device.  Therefore, drop the switch
statement entirely and just check for POD_monitor_level, ignoring
unknown system parameter changes.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>