configs: remove default sampling rate and channel entries for bt a2dp

 Remove default setting of sampling rate to 48K and stereo channel
 for bt a2dp as support for multiple sampling rates and channels
 over a2dp is added and being set from hal.

Change-Id: If31d65c53b562e0e265b5ed542658f219f0e80b2
CRs-Fixed: 2205297