am: regroup debug conditionals in OomAdjuster

TODO: check following tests:
com.android.server.am.BackgroundRestrictionTest#testInitialLevels
com.android.server.am.BackgroundRestrictionTest#testTogglingStandbyBucket
com.android.server.am.MockingOomAdjusterTests#testUpdateOomAdj_UidIdle_StopService

Bug: 425766486
Test: m services.core
Test: atest MockingOomAdjusterTests OomAdjusterTests
Test: atest FrameworksServicesTestsRavenwood_ProcessStateController
Test: atest FrameworksMockingServicesTests_android_server_am_broadcast
Flag: EXEMPT pure refactor

Change-Id: I672ec55334a52c931a44a616e7430e3d63d95806