phone: let the screen sleep while Gearslip is open

The car screen is its own display, so the phone's screen doesn't need to stay on, and it no
longer stays on with no car connected.

gearslip/src/main/java/app/seb3thehacker/gearslip/GearslipActivity.kt

@@ -14,7 +14,6 @@ import android.os.ParcelFileDescriptor
 import android.provider.Settings
 import android.view.MotionEvent
 import android.view.Surface
-import android.view.WindowManager
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
 import androidx.compose.runtime.collectAsState
@@ -141,7 +140,6 @@ class GearslipActivity : ComponentActivity(), Projection {
         // is both a bad first impression and unreliable: Android does not consistently show more
         // than one system permission dialog fired back-to-back, which was silently dropping some.
         enableEdgeToEdge()
-        window.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
 
         GearslipLog.init(this)
         GearslipLog.installCrashHandler()