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.

CRs-Fixed: 2205297
Change-Id: If31d65c53b562e0e265b5ed542658f219f0e80b2