Enable code shrinking (dead code removal) on Launcher3QuickStepGo app

Bug: 112042795
Test: Manual testing

I found following effect of shrinking on the apk:

Launcher3QuickStepGo.apk            4925099 bytes
Launcher3QuickStepGo_Proguard.apk   2619051 bytes

We get total saving of 2306048 bytes in apk size.

Change-Id: I75abedc05e5d04967928e73f02bcc78608f52ac0