ALSA: hda - Remove AZX_DCAPS_POSFIX_COMBO

It turned out that the COMBO position fix mode is rather more harmful,
and it got reverted (with the replacement of runtime->delay
calculation) recently.  Hence we can get rid of AZX_DCAPS_POSFIX_COMBO
as well.

It's still possible to pass this mode via position_fix module option,
in case where this really helps on weird machines (who knows).

Signed-off-by: Takashi Iwai <tiwai@suse.de>