Kill most of phutil_escape_html()

Summary:
This resolves lots of double escaping.
We changed most of `phutil_render_tag(, , $s)` to `phutil_tag(, , $s)` which means that `$s` is now auto-escaped.
Also `pht()` auto escapes if it gets `PhutilSafeHTML`.

Test Plan: None.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2432

Differential Revision: https://secure.phabricator.com/D4889

src/applications/auth/controller/PhabricatorLoginController.php

@@ -247,8 +247,7 @@ final class PhabricatorLoginController
         $title = pht("Login or Register with %s", $provider_name);
         $body = pht('Login or register for Phabricator using your %s account.',
           $provider_name);
-        $button = pht("Login or Register with %s",
-          phutil_escape_html($provider_name));
+        $button = pht("Login or Register with %s", $provider_name);
       } else {
         $title = pht("Login with %s", $provider_name);
         $body = hsprintf(
@@ -259,7 +258,7 @@ final class PhabricatorLoginController
           pht(
             'You can not use %s to register a new account.',
             $provider_name));
-        $button = pht("Log in with %s", phutil_escape_html($provider_name));
+        $button = pht("Log in with %s", $provider_name);
       }
 
       $auth_form = new AphrontFormView();