Refine Settings proguard rules

Avoid keeping unused library classes and remove several redundant rules.
This saves ~700KB dex and a modest amount of Jetpack resources that are
no longer referenced.

Bug: 248580093
Test: m + presubmit + atest SettingsUnitTests
Change-Id: Ic2398345a35117ccab433d2fd1c31c0f453ed77c
1 file changed