Don't moveToRestState from onTaskAppeared

There's a possible race here where we call moveToRestState before
Launcher is actually stopped, so it starts to animate the state
change, causing a visual jump before it gets stopped. We already call
moveToRestState in StatefulActivity#onStop, so this one shouldn't be
necessary anyway.

Test: Enable Winscope tracing, quick switch from app A to app B; before
this change, 9/10 times it would repro the jump in the bug, 0/10 times
after this fix. (Also verified through debug logging.)
Fixes: 244583136

Change-Id: I656b028f26a64f872960cb3fe87c39b097431511