Re-enable PeripheralBatteryNotifier tests that were flaky with mus.

"mus" doesn't exist anymore, so it should be safe to re-enable back
these tests.

Bug: 765794
Change-Id: I8efa18d8d514d902e9f7654da8a810ed633481e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1729790Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Commit-Queue: Alberto Herrera <ahrfgb@google.com>
Cr-Commit-Position: refs/heads/master@{#682927}

ash/system/power/peripheral_battery_notifier_unittest.cc

@@ -238,8 +238,7 @@ TEST_F(PeripheralBatteryNotifierTest, ExtractBluetoothAddress) {
   EXPECT_TRUE(non_bluetooth_device_info.bluetooth_address.empty());
 }
 
-// TODO(crbug.com/765794): Flaky on ash_unittests with mus.
-TEST_F(PeripheralBatteryNotifierTest, DISABLED_DeviceRemove) {
+TEST_F(PeripheralBatteryNotifierTest, DeviceRemove) {
   battery_notifier_->PeripheralBatteryStatusReceived(kTestBatteryPath,
                                                      kTestDeviceName, 5);
   EXPECT_EQ(1u, battery_notifier_->batteries_.count(kTestBatteryId));
@@ -251,8 +250,7 @@ TEST_F(PeripheralBatteryNotifierTest, DISABLED_DeviceRemove) {
               nullptr);
 }
 
-// TODO(crbug.com/765794): Flaky on ash_unittests with mus.
-TEST_F(PeripheralBatteryNotifierTest, DISABLED_StylusNotification) {
+TEST_F(PeripheralBatteryNotifierTest, StylusNotification) {
   const std::string kTestStylusBatteryPath =
       "/sys/class/power_supply/hid-AAAA:BBBB:CCCC.DDDD-battery";
   const std::string kTestStylusName = "test_stylus";