Remove flag doze_brightness_float

Also remove all the int methods. If the float config is undefined, the int config is read and converted to float in DozeScreenBrightness.

Bug: 409605068
Flag: EXEMPT removing com.android.server.display.feature.flags.doze_brightness_float
Test: DreamServiceTest, AlwaysOnDisplayPolicyTest, DozeScreenBrightnessTest, NotificationShadeWindowControllerImplTest, DozeServiceHostTest, DreamManagerServiceTests, PowerManagerServiceTest, DisplayDeviceConfigTest
Change-Id: I054f5da90d3e9e88e516be1114f6f0a6c774ad31