Avoid adjusting top focused root task while clear task

Top focused root task was updated while clear task for reuse, which
isn't necessary. This was happening after 046523ce merged.

Also avoid resuming the top activity in next focused
root task to prevent additional top-resumed-activity state changes.

Bug: 160613519
Test: asit/perf/junit/jank_systemui_test

Change-Id: I8ddbfc3b0a62ddb29833d324e42812ed0dc096db