remove user api conferences context from routes

the routes don't actually work

test plan:
* specs

closes #LA-1055

Change-Id: I23b5b888042c5d3d3920c7d8fb60fa5acd6fcce1
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/238040
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Clint Furse <cfurse@instructure.com>
Product-Review: James Williams <jamesw@instructure.com>

config/routes.rb

@@ -2015,7 +2015,7 @@ CanvasRails::Application.routes.draw do
     end
 
     scope(controller: :conferences) do
-      %w(user course group).each do |context|
+      %w(course group).each do |context|
         prefix = "#{context}s/:#{context}_id/conferences"
         get prefix, action: :index, as: "#{context}_conferences"
         post "#{prefix}", action: :create