SystemUI: Allow disabling BrightlineFalsingManager with config flag

The anti-falsing implementation does not work well on some
devices, and regularly prevents easy swipe to unlock or to
pattern / pin on the keyguard lockscreen, requiring multiple
attempts until accepted.

Use existing config_lockscreenAntiFalsingClassifierEnabled flag
to allow it to be disabled. By default it's enabled.

Change-Id: Ib91fc2386f70f56aad68a0f7ad2e3445fbb42d79