[LowLightBoost] Fix low light boost test

- remove logic to check for non-null value of low light boost state when
  ae mode is set to low light boost brightness priority mode
- the default value of low light boost state is always 'inactive'

Flag: com.android.internal.camera.flags.camera_ae_mode_low_light_boost
Test: atest android.hardware.camera2.cts.CaptureResultTest
Bug: 346188277
Change-Id: Id7e54e5baecc5cab29e5f7a06bf82bee62e68da4