sound: usb-audio: remove check_hw_params_convention()

This removes the check_hw_params_convention() function because
1) it is not necessary, as the hw_rule_* functions also work correctly
   (i.e., as no-ops) when the device supports all combinations of the
   audio format parameters; and
2) it would become too complex when adding a fourth altsetting-dependent
   hardware parameter, as this would require another three loops to
   check dependecies with rate/channels/format.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>