Remove Named interface (#26913)

`Named` is implemented by every `Method` and future implementations
should implement the method too.

services/auth/oauth2.go

@@ -22,7 +22,6 @@ import (
 // Ensure the struct implements the interface.
 var (
 	_ Method = &OAuth2{}
-	_ Named  = &OAuth2{}
 )
 
 // CheckOAuthAccessToken returns uid of user from oauth token