Do not set side stage position

c67d535e, Consolidate adjacent launch to update the stage
position, but it conflicts with startShort case. This CL doesn't
set the side stage during the handleRequest to prevent setting
the wrong stage position.

Bug: 286540547
Test: atest WMShellFlickerTests:EnterSplitScreenByDragFromShortcut
Change-Id: I02a87a404b9ecc6a3ceac31531d670f55d4cc9d4