Remove Named interface (#26913)

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

services/auth/httpsign.go

@@ -23,7 +23,6 @@ import (
 // Ensure the struct implements the interface.
 var (
 	_ Method = &HTTPSign{}
-	_ Named  = &HTTPSign{}
 )
 
 // HTTPSign implements the Auth interface and authenticates requests (API requests