chore: remove more oauth refrences (#687)

* chore: Removing Test Related To Deprecated Endpoint - OAuth

* removing more oauth refrences

Author: KobeBrooks

lib/twilio-ruby/rest/client.rb

@@ -116,12 +116,6 @@ def notify
             def numbers
                 @numbers ||= Numbers.new self
             end
-            ##
-            # Access the Oauth Twilio Domain
-            def oauth
-                @oauth ||= Oauth.new self
-            end
-            ##
             # Access the Preview Twilio Domain
             def preview
                 @preview ||= Preview.new self