f_uac1: Remove unwanted descriptors for volume/mute support

Remove unwanted descriptors like dummy mic input descriptor and
related feature unit descriptor as those are not required for
volume/mute support for mic and speaker paths.

Change-Id: I93b2dbe114183212570229c3ccb89a36a4008917
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>