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
diff --git a/system/stack/BUILD.gn b/system/stack/BUILD.gn
index 70e7eb4..9dc4670 100644
--- a/system/stack/BUILD.gn
+++ b/system/stack/BUILD.gn
@@ -112,6 +112,7 @@
     "btm/btm_ble_gap.cc",
     "btm/btm_ble_multi_adv.cc",
     "btm/btm_ble_privacy.cc",
+    "btm/btm_ble_scanner.cc",
     "btm/btm_client_interface.cc",
     "btm/btm_dev.cc",
     "btm/btm_devctl.cc",