Fix config-migration text for dashboard options

Summary:
The commit which added checks for the old homepage options (now in
Dashboard) in rP9d9a47e9cf, added them to the auth section, where they
would present:
  This option has been migrated to the "Auth" application. Your old
  configuration is still in effect, but now stored in "Auth" instead of
  configuration. Going forward, you can manage authentication from the
  web UI.

Remove them from the moved-to-Auth list, and coalesce the multiple
definitions of the help text into one.

Test Plan:
 - set maniphest.priorities.unbreak-now to something
 - observe the setup issue reported
 - hope it tells you the right thing

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley, chad

Differential Revision: https://secure.phabricator.com/D16576

Author: fooishbar

src/applications/config/check/PhabricatorExtraConfigSetupCheck.php

@@ -143,9 +143,6 @@ public static function getAncientConfig() {
       'phabricator.auth-permanent',
       'phabricator.application-id',
       'phabricator.application-secret',
-      'maniphest.priorities.unbreak-now',
-      'maniphest.priorities.needs-triage',
-      'welcome.html',
     );
 
     $ancient_config = array_fill_keys($auth_config, $reason_auth);
@@ -197,6 +194,10 @@ public static function getAncientConfig() {
       'The "Re: Prefix" and "Vary Subjects" settings are now configured '.
       'in global settings.');
 
+    $dashboard_reason = pht(
+        'This option has been removed, you can use Dashboards to provide '.
+        'homepage customization. See T11533 for more details.');
+
     $ancient_config += array(
       'phid.external-loaders' =>
         pht(
@@ -336,17 +337,9 @@ public static function getAncientConfig() {
         'This option has been replaced with `ui.logo`, which provides more '.
         'flexible configuration options.'),
 
-      'welcome.html' => pht(
-        'This option has been removed, you can use Dashboards to provide '.
-        'homepage customization. See T11533 for more details.'),
-
-      'maniphest.priorities.unbreak-now' => pht(
-        'This option has been removed, you can use Dashboards to provide '.
-        'homepage customization. See T11533 for more details.'),
-
-      'maniphest.priorities.needs-triage' => pht(
-        'This option has been removed, you can use Dashboards to provide '.
-        'homepage customization. See T11533 for more details.'),
+      'welcome.html' => $dashboard_reason,
+      'maniphest.priorities.unbreak-now' => $dashboard_reason,
+      'maniphest.priorities.needs-triage' => $dashboard_reason,
 
     );