ASoC/mfd: twl4030: Remove set_hs_extmute callback from platform data

We no longer have users for the set_hs_extmute callback which has been
replaced by hs_extmute_gpio so the codec driver can handle the external
mute if it is needed by the board.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>