File sharing: remove unused background parameters that were triggering lint

Signed-off-by: Álvaro Brey Vilas <alvaro.brey@nextcloud.com>

src/main/res/layout/file_details_sharing_menu_bottom_sheet_fragment.xml

@@ -24,7 +24,6 @@
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
-    android:background="@color/bg_default"
     android:orientation="vertical"
     android:paddingTop="@dimen/standard_padding">
 

src/main/res/layout/file_details_sharing_process_fragment.xml

@@ -24,7 +24,6 @@
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="@color/bg_default"
     android:focusable="true"
     android:focusableInTouchMode="true">
 

src/main/res/layout/quick_sharing_permissions_bottom_sheet_fragment.xml

@@ -22,7 +22,6 @@
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
-    android:background="@color/bg_default"
     android:paddingTop="@dimen/standard_padding"
     android:paddingBottom="@dimen/standard_padding"
     android:orientation="vertical">