Fix proguard flags to retain FindNearby class.

Bug: 3140836
diff --git a/proguard.flags b/proguard.flags
index 0e1b428..88da024 100644
--- a/proguard.flags
+++ b/proguard.flags
@@ -4,3 +4,5 @@
 -keep class com.android.settings.*Settings
 -keep class com.android.settings.wifi.*Settings
 -keep class com.android.settings.deviceinfo.*
+-keep class com.android.settings.bluetooth.*
+