[Expressive design] Remove extra background of MainSwitchPreference.

Bug: 349681531
Flag: EXEMPT bug fix
Test: Visual
Change-Id: Ib3a0e81b0bd1efbe85ce3992d343ae312e610dd3

res/xml/mobile_network_settings.xml

@@ -18,7 +18,7 @@
     xmlns:settings="http://schemas.android.com/apk/res-auto"
     android:key="mobile_network_pref_screen">
 
-    <com.android.settings.spa.preference.ComposePreference
+    <com.android.settings.spa.preference.ComposeMainSwitchPreference
         android:key="use_sim_switch"
         settings:controller="com.android.settings.network.telephony.MobileNetworkSwitchController"/>
 

src/com/android/settings/spa/preference/ComposePreference.kt

@@ -26,6 +26,14 @@ import androidx.preference.Preference
 import androidx.preference.PreferenceViewHolder
 import com.android.settings.R
 import com.android.settingslib.spa.framework.theme.SettingsTheme
+import com.android.settingslib.widget.GroupSectionDividerMixin
+
+open class ComposeMainSwitchPreference @JvmOverloads constructor(
+    context: Context,
+    attrs: AttributeSet? = null,
+    defStyleAttr: Int = 0,
+    defStyleRes: Int = 0,
+) : ComposePreference(context, attrs, defStyleAttr, defStyleRes), GroupSectionDividerMixin
 
 open class ComposePreference @JvmOverloads constructor(
     context: Context,