Fix windowless surface being removed too early

Similar to remove starting window with shell transition, the windowless
starting surface should only being removed until the start transaction
has applied in Shell.

Flag: EXEMPT bugfix
Bug: 370035244
Test: set animation duration to 0, trigger close transition with back
gesture several times, verify no flickering occur.

Change-Id: I97ecd340baf80f0de9fa11aa44f06e5cf6c5c8c5