Remove splash screen and window wallpaper

Both features used ?attr/colorSurface as the base layer of
a layer-list drawable set as android:windowBackground. That
attribute is resolved during drawable inflation, before the
theme is fully attached on certain GPU drivers. This is the
root cause of the rendering glitches reported since 1.73.0
in #655.

The proper fix for Material You is to reference ?attr/colorSurface
directly in the theme style, where the framework resolves it
at Activity level. But both backgrounds were layer-lists (color
and bitmap), so keeping them would have required moving the bitmaps
out of the window background and into every affected layout. Which
would have been a significant churn for purely decorative elements.

Removing them is the simpler and more correct outcome: the theme
now sets android:windowBackground to ?attr/colorSurface directly,
which works reliably everywhere and honours Material You dynamic
colours without workarounds.

app/src/main/AndroidManifest.xml

@@ -46,7 +46,7 @@
 		android:theme="@style/AppTheme">
 		<activity
 			android:name=".activity.SplashActivity"
-			android:theme="@style/SplashTheme"
+			android:theme="@style/AppTheme"
 			android:exported="true">
 			<intent-filter>
 				<action android:name="android.intent.action.MAIN"/>

app/src/main/res/drawable/background_splash.xml

@@ -1,8 +0,0 @@
-<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
-	<item android:drawable="?attr/colorSurface"/>
-	<item>
-		<bitmap
-			android:gravity="center"
-			android:src="@drawable/logo"/>
-	</item>
-</layer-list>

app/src/main/res/drawable/background_window.xml

@@ -1,8 +0,0 @@
-<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
-	<item android:drawable="?attr/colorSurface"/>
-	<item>
-		<bitmap
-			android:gravity="top|right"
-			android:src="@drawable/wallpaper"/>
-	</item>
-</layer-list>

app/src/main/res/values/styles.xml

@@ -1,6 +1,6 @@
 <resources>
 	<style name="AppTheme" parent="Theme.Material3.Dark.NoActionBar">
-		<item name="android:windowBackground">@drawable/background_window</item>
+		<item name="android:windowBackground">?attr/colorSurface</item>
 		<item name="android:statusBarColor">@android:color/transparent</item>
 		<item name="android:navigationBarColor">@android:color/transparent</item>
 		<item name="colorPrimary">@color/legacy_accent</item>
@@ -27,10 +27,7 @@
 		<item name="windowActionModeOverlay">true</item>
 		<item name="preferenceTheme">@style/PreferenceThemeOverlay.v14.Material</item>
 	</style>
-	<style name="SplashTheme" parent="@style/AppTheme">
-		<item name="android:windowBackground">@drawable/background_splash</item>
-	</style>
-	<style name="AppToolbar" parent="Widget.Material3.Toolbar">
+<style name="AppToolbar" parent="Widget.Material3.Toolbar">
 		<item name="android:background">@android:color/transparent</item>
 		<item name="background">@android:color/transparent</item>
 		<item name="titleTextColor">?attr/colorOnSurface</item>