Remove all associaitons when forget a device in Settings

The associations will be removed one forget the device.

Test: manually test
Bug: 365613753
Flag: com.android.settings.flags.enable_remove_association_bt_unpair
Change-Id: Ic2224952b6f8e776ffcf07ce4fa6953a98475490

aconfig/settings_bluetooth_declarations.aconfig

@@ -54,3 +54,11 @@ flag {
       purpose: PURPOSE_BUGFIX
   }
 }
+
+flag {
+  name: "enable_remove_association_bt_unpair"
+  is_exported: true
+  namespace: "companion_device_manager"
+  description: "Allow to disassociate when to forget a BT pair device"
+  bug: "365613753"
+ }