Clean up the mLastSentTaskInfos entry

mLastSentTaskInfos, A map maintains the relationship between task and
runningTaskInfo. RunningTaskInfo was put into the map during the
TaskOrganizerController#dispatchTaskInfoChanged, but never remove it.
This CL removes the entry while the task is vanished.

Bug: 199523354
Test: atest TaskOrganizerTest
            ShellTaskOrganizerTests
            PipTaskOrganizerTest
Change-Id: I55b1caff1ff3fe43db12350659f0a066ed4ef5dd