Fix the art work of lockscreen cannot be removed

The root cause is that mMediaNotificationKey is cleared right after it is set.
It makes the media art work cannot be cleared since there is no
notification that match the mMediaNotificationKey which is already
cleared to null.

Only clear media session related data inside the controller check.

Test: runtest systemui
Test: manual
Change-Id: Iae43c502b90f73e57fae7150e15ef89eb18b096c
Fixes: 78204513