Show disable dialog box when none is selected

Also remove from CMPP since that will be
hidden.

Test: ondevice
Bug: 281147573
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:16d3b54aaf802c66be439bf65c877cba60c4390d)
Merged-In: Ic2b59c42ed4ddbc83a770b8bb99c641d2f1a383d
Change-Id: Ic2b59c42ed4ddbc83a770b8bb99c641d2f1a383d

src/com/android/settings/applications/credentials/DefaultCombinedPicker.java

@@ -273,8 +273,13 @@ public class DefaultCombinedPicker extends DefaultAppPickerFragment {
 
     @Override
     protected CharSequence getConfirmationMessage(CandidateInfo appInfo) {
+        // If we are selecting none then show a warning label.
         if (appInfo == null) {
-            return null;
+            final String message =
+                    getContext()
+                            .getString(
+                                    R.string.credman_confirmation_message);
+            return Html.fromHtml(message);
         }
         final CharSequence appName = appInfo.loadLabel();
         final String message =