🚧 Temporarily remove check_auth_method and check_auth_args [WIP]

The problem is that not every SASL mechanism uses username and password
nor do they all authenticator take two positional parameters.  It's a
little more complicated to verify that 1) the authenticator exists, and
2) we've supplied all required parameters.

TODO: However, since we already know the authenticator arguments
up-front, we can simply create the authenticator object and rely on the
its initializer to raise ArgumentError for missing args.

lib/net/smtp.rb

@@ -634,10 +634,6 @@ def tcp_socket(address, port)
 
     def do_start(helo_domain, user, secret, authtype)
       raise IOError, 'SMTP session already started' if @started
-      if user or secret
-        check_auth_method(authtype || DEFAULT_AUTH_TYPE)
-        check_auth_args user, secret
-      end
       s = Timeout.timeout(@open_timeout, Net::OpenTimeout) do
         tcp_socket(@address, @port)
       end
@@ -833,8 +829,6 @@ def open_message_stream(from_addr, *to_addrs, &block)   # :yield: stream
     DEFAULT_AUTH_TYPE = :plain
 
     def authenticate(user, secret, authtype = DEFAULT_AUTH_TYPE)
-      check_auth_method authtype
-      check_auth_args user, secret
       authenticator = Authenticator.auth_class(authtype).new(self)
       critical { authenticator.auth(user, secret) }
     end
@@ -859,27 +853,6 @@ def auth(*args, mechanism: nil, **kwargs, &block)
       }
     end
 
-    private
-
-    def check_auth_method(type)
-      unless Authenticator.auth_class(type)
-        raise ArgumentError, "wrong authentication type #{type}"
-      end
-    end
-
-    def auth_method(type)
-      "auth_#{type.to_s.downcase}".intern
-    end
-
-    def check_auth_args(user, secret, authtype = DEFAULT_AUTH_TYPE)
-      unless user
-        raise ArgumentError, 'SMTP-AUTH requested but missing user name'
-      end
-      unless secret
-        raise ArgumentError, 'SMTP-AUTH requested but missing secret phrase'
-      end
-    end
-
     #
     # SMTP command dispatcher
     #