[DeviceService] Replace content browser test with service test for BatteryMonitorImpl

services/device/unittest_manifest.json

 {
   "name": "device_unittests",
   "display_name": "Device Service Unittests",
   "interface_provider_specs": {
     "service_manager:connector": {
       "provides": {
         "service_manager:service_factory": [
           "service_manager::mojom::ServiceFactory"
         ]
       },
       "requires": {
-        "device": [ "device:vibration" ]
+        "device": [
+          "device:battery_monitor",
+          "device:vibration"
+        ]
       }
     }
   }
 }