Stop removing all APP_STANDBY_BUCKET_CHANGED messages.

APP_STANDBY_BUCKET_CHANGED messages are for single apps, so it doesn't
make sense to remove all messages whenever any app's standby bucket
changes.

Bug: 193918191
Test: N/A
Change-Id: I981cd3be3cd381c6d00f06e3da9f8e67f157a26b