Update proguard rules to remove aggressive keeping.
Update proguard rules to remove aggressive keeping.

They were necessary when we were running proguard as part of building
our aar, to keep all of our frontend API.

Now that the aar is being proguarded via consumerProguardRules, we no
longer need this as proguard will correctly keep the API that is
actually being used.

Bug: 161836669
Test: Builds
Change-Id: I59423c3dbed12e63e08fbda0bc7a9b88513f2361

AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx