Not allowing foreground services to be cleared as children

forground service notifications could simply be cleared
when they were sent as notification children and then
the summary was cancelled.

This also cleans up the logic in systemui and only removes
the child if allowed.

The clear all button could also show under certain conditions
where it shouldn't have been shown.

Change-Id: I85998b5342bd75425cc6d68e96391299c4f3d83d
Test: manual
Bug: 33766648