Cleanup for theme picker

- Remove the ThemePreviewPage and related layout/dimens.
- Remove the v2 suffix, they are the v1 now.

Test: Build and run successfully
Bug: 151285476
Change-Id: Ie79b8676c3f28cbec77c04db65c16445276a3345
diff --git a/res/layout/fragment_theme_picker.xml b/res/layout/fragment_theme_picker.xml
index c61c389..a773207 100644
--- a/res/layout/fragment_theme_picker.xml
+++ b/res/layout/fragment_theme_picker.xml
@@ -46,7 +46,7 @@
                 app:layout_constraintHeight_max="@dimen/preview_pager_max_height"
                 app:layout_constraintVertical_bias="0.0"
                 app:layout_constraintHeight_percent="@dimen/preview_pager_maximum_height_ratio">
-                <include layout="@layout/theme_preview_card_v2"/>
+                <include layout="@layout/theme_preview_card"/>
             </FrameLayout>
 
             <androidx.recyclerview.widget.RecyclerView