Restore trimMemory behaviour from T

When we moved trimming code to ResourceTrimmer in I84637049a106a94bf9f06c5261c2941b55db4ba0, we also moved trimMemory(ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN) which happens after unlock from StatusBarKeyguardViewManager to the ResourceTrimmer behind a TRIM_FONT_CACHES_AT_UNLOCK flag.

Now that we've disabled TRIM_FONT_CACHES_AT_UNLOCK, this also disabled the trimMemory call we were doing since way before Android U.

To full restore pre-U trim font behaviour, this call should not be flag guarded behind the font caching flag.

Bug: 275486055
Bug: 290898642
Test: Updated unit tests
Change-Id: I677855fff144a53d212b65575111491c78803817