Don't store doze manual brightness in setting

This bug is only visible with the refactor DPC flag enabled - that's because the FallbackStrategy is used and it sets updateScreenBrightnessSetting to true, even though it later gets overridden with a different brightness strategy.

Bug: 349296625
Flag: EXEMPT bugfix
Test: atest DisplayPowerControllerTest
Change-Id: Ica2a345658059394b454a5b13dd5d9e8606b837c