Cleanup trim caches flags

Enabling those flags creates too much jank so we're not going to roll
them out. Clean up the code behind them.

Bug: 283203305
Bug: 322143614

Flag: com.android.systemui.trim_resources_with_background_trim_at_lock_launch
Test: unit tests present
Change-Id: I2310f14145e93027b4cb6229e7811030f3087aef