Removed unused functions

Removed unused functions and defines that are not needed:
 - l2c_bcst_msg()
 - GAP_ConnBTWrite()
 - gap_proc_btu_event()
 - AVDT_WriteDataReq()
 - L2CAP_BCST_MIN_OFFSET
 - L2CAP_BCST_OVERHEAD
 - AVDT_MAX_MEDIA_SIZE
 - LOG_NDDEBUG in btif/src/bluetooth.c

Bug: 28068134
Change-Id: If0edda2bf86caf83027db2c897537c82a0d80667