Remove unnecessary reader sheet backgrounds

app/src/main/res/layout-land/reader_color_filter_sheet.xml

@@ -3,7 +3,6 @@
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
-    android:background="?attr/colorSurface"
     android:baselineAligned="false"
     android:orientation="horizontal">
 

app/src/main/res/layout/reader_color_filter_sheet.xml

@@ -2,7 +2,6 @@
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="?attr/colorSurface"
     android:orientation="vertical">
 
     <FrameLayout

app/src/main/res/layout/reader_page_sheet.xml

@@ -3,7 +3,6 @@
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
-    android:background="?attr/colorSurface"
     android:orientation="vertical">
 
     <LinearLayout

app/src/main/res/layout/reader_settings_sheet.xml

@@ -4,7 +4,6 @@
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="?attr/colorSurface"
     android:clipToPadding="false"
     android:orientation="vertical"
     android:paddingStart="24dp"