Reload task list when task is removed

Instead of individually removing tasks,
ask for all tasks to get accurate list.
This method is invoked whenever user presses
back on a root activity, which causes the task to
be killed from perspective of the activity.

Test: Visually inspected, recent task no longer
disappears.

Fixes: 135687618
Change-Id: I1c135673ae987016db5df0b83f5ea8e345d3c7c1