Remove sliceable attribute from biometric preference controllers.

This removes the top-level UI switch on some of the boolean preference settings.

Bug: 193438173
Test: atest com.android.settings.biometrics
Change-Id: If1cd2cb9ae456021fcdf0efc5002db4a083b9689

src/com/android/settings/biometrics/face/FaceSettingsPreferenceController.java

@@ -46,4 +46,9 @@ public abstract class FaceSettingsPreferenceController extends TogglePreferenceC
         return RestrictedLockUtilsInternal.checkIfKeyguardFeaturesDisabled(
                 mContext, DevicePolicyManager.KEYGUARD_DISABLE_FACE, mUserId);
     }
+
+    @Override
+    public final boolean isSliceable() {
+        return false;
+    }
 }