Remove manual call to stash takbar from within onTaskbarIconLaunched.

Taskbar does not know if the icon clicked will result in a translucent
activity. After this change, taskbar app stashing logic is now the same
between taskbar and home launches.

We should still stash after split screen, because in the case of
translucent activity the background becomes opaque.

Fixes: 354627538
Test: Pause app in hotseat, go to overview, launch paused app
      note that taskbar does not go away
Flag: EXEMPT bugfix
Change-Id: I3d3ed7a6ca10090c7207b45d0b272dc4fc928e32