Only clear shared starting data for starting window owner.

Issue symptom:
1. Start Activity A
2. A start Activity B, and both move to TaskFragment for AE.
3. Activity B start Activity C.
4. Activity C stopped before Activity A drawn. sharedStartingData being
removed due to C stopped.
5. Activity A report drawn, but it is unable to remove starting window.
The activity B should not clear mSharedStartingData, unless it is the
owner of startingData.

Bug: 330478990
Test: follow issue description.
Change-Id: I66e3d271c41019b4243ceda30ee0d9fe549335b0