floss: build: Add btm_ble_scanner and remove leaudio

Add missing btm_ble_scanner.cc to BUILD and remove leaudio entirely from
build. LeAudio was in a half-building state before and new changes were
breaking the build so remove it entirely.

Bug: 216863527
Tag: #floss
Test: Build on ChromeOS
Change-Id: Ic5aeec3e2464d8adb0cda5582fde8e3a1921c45e
Merged-In: Ic5aeec3e2464d8adb0cda5582fde8e3a1921c45e