Fix split recent thumbnail disappear

This bug should caused by we reset side stage position after
dismissing split screen. It might cause race condition but still
do not know why it cause such symptom.
Because this reset action is just purpuse to make every time user
launch adjacent the new task is expand from right or bottom side,
remove this is no risk.

Fix: 243628874
Test: manaul
Test: pass existing tests
Change-Id: I171aafe775484a6b25b343eeea1b1f3cbc99b452