Merge branch 'mjang-doc-note-ultraauth-removal' into 'master'

Note removal of UltraAuth integration

See merge request gitlab-org/gitlab!31472

doc/administration/auth/README.md

@@ -32,3 +32,6 @@ providers:
 - [Shibboleth](../../integration/shibboleth.md)
 - [Smartcard](smartcard.md) **(PREMIUM ONLY)**
 - [Twitter](../../integration/twitter.md)
+
+NOTE: **Note:**
+UltraAuth has removed their software which supports OmniAuth integration. We have therefore removed all references to UltraAuth integration.