Move to a single dropdown background for the search dialog. This one

is full-screen width but has rounded corners on the bottom so it doesn't
look crappy if the list is not full-screen height. This was already
being used for in-app search, so I just got rid of the old global search
background and use the in-app one for everything.

By removing the lines in SearchDialog, I'm causing it to rely on the
value specified for the dropdown background in
frameworks/base/core/res/res/layout/search_bar.xml.

core/java/android/app/SearchDialog.java

@@ -560,12 +560,8 @@ public class SearchDialog extends Dialog implements OnItemClickListener, OnItemS
 
         if (mGlobalSearchMode) {
             mSearchAutoComplete.setDropDownAlwaysVisible(true);  // fill space until results come in
-            mSearchAutoComplete.setDropDownBackgroundResource(
-                    com.android.internal.R.drawable.search_dropdown_background);
         } else {
             mSearchAutoComplete.setDropDownAlwaysVisible(false);
-            mSearchAutoComplete.setDropDownBackgroundResource(
-                    com.android.internal.R.drawable.search_dropdown_background_apps);
         }
 
         // attach the suggestions adapter, if suggestions are available