[MM-57085] Remove UseNewSAMLLibrary experimental setting (#26392)

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/enterprise.go

@@ -74,10 +74,10 @@ func RegisterCloudInterface(f func(*Server) einterfaces.CloudInterface) {
 	cloudInterface = f
 }
 
-var samlInterfaceNew func(*App) einterfaces.SamlInterface
+var samlInterface func(*App) einterfaces.SamlInterface
 
-func RegisterNewSamlInterface(f func(*App) einterfaces.SamlInterface) {
-	samlInterfaceNew = f
+func RegisterSamlInterface(f func(*App) einterfaces.SamlInterface) {
+	samlInterface = f
 }
 
 var notificationInterface func(*App) einterfaces.NotificationInterface