Move some logic of removeTask() into TaskRecord.

Follow up from 891146c6a6e40f40d9e9ca34378389a5aa6a53a7 to move some
logic into TaskRecord.

It removes seemingly unnecessary onActivityRemovedFromStack(), and also
encapsulates mLRUActivities into ActivityStack itself by moving stack
dump logic into ActivityStack.

Bug: 119259346
Test: Unit tests pass. go/wm-smoke. dumpsys activity activities doesn't
change.
Change-Id: Ic76fe64afd048a4fb489fd76125d072d4432da07
3 files changed