Do not cancel animations when switching.

Was canceling ongoing animations when starting a new animation which
caused the window of the first animation to restart. This looked
janky. The original cancellation was put in to stop the incorrect
animation being selected when quickly switching between an incoming
app and the homescreen. Reversing the cancellation no longer exposes
the original problem it was put in to fix.

One way to duplicate what this is fixing.
1. Slow down animations to 10x.
2. Run ApiDemos/App/Alert Dialogs/List dialog
3. Tap outside the list dialog and then tap the home button.
Tapping outside the list dialog causes the list dialog to animate
away. Tapping the home button then causes the app to animate away.
Before this fix the list dialog would revert to full size before
the app animates away. With this fix the list dialog continues its
original animation as the app animates away.

Fixes bug 6600726.

Change-Id: I29c940254808a321c3b6c2e4f4b7c78a72b47899