Don't animate category spinner hiding

This caused the entire list view to e animated when navigating
back to the Available tab. Tried switching the `animateLayoutChanged=true`
to a child view only containing the category spinner, but this is not how
the animation handling works. It needs to animate both the thing being
hidden/shown, and also the next sibling of that thing to work properly.
Thus, moving the spinner to its own child and leaving the list didn't work.

F-Droid/res/layout/available_app_list.xml

@@ -2,8 +2,7 @@
 <RelativeLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
-    android:layout_height="match_parent"
-    android:animateLayoutChanges="true">
+    android:layout_height="match_parent">
 
     <Spinner
         android:id="@+id/category_spinner"