Do not use the dynamic :action segment on Omniauth routes.

This was deprecated on rails/rails#23980.

We now generate scope and provider specific routes, like `user_facebook_omniauth_callback`
or `user_github_omniauth_callback`.

We could deprecate the `omniauth_authorize_path` in favor of the generated routes, but
the `shared/links.html.erb` depends on it to generate all omniauth links at once.

Closes #3983.

test/omniauth/url_helpers_test.rb

@@ -1,23 +1,21 @@
 require 'test_helper'
 
 class OmniAuthRoutesTest < ActionController::TestCase
-  ExpectedUrlGeneratiorError = ActionController::UrlGenerationError
-
   tests ApplicationController
 
   def assert_path(action, provider, with_param=true)
     # Resource param
     assert_equal @controller.send(action, :user, provider),
-                 @controller.send("user_#{action}", provider)
+                 @controller.send("user_#{provider}_#{action}")
 
     # With an object
     assert_equal @controller.send(action, User.new, provider),
-                 @controller.send("user_#{action}", provider)
+                 @controller.send("user_#{provider}_#{action}")
 
     if with_param
       # Default url params
       assert_equal @controller.send(action, :user, provider, param: 123),
-                   @controller.send("user_#{action}", provider, param: 123)
+                   @controller.send("user_#{provider}_#{action}", param: 123)
     end
   end
 
@@ -32,7 +30,7 @@ class OmniAuthRoutesTest < ActionController::TestCase
   test 'should generate authorization path' do
     assert_match "/users/auth/facebook", @controller.omniauth_authorize_path(:user, :facebook)
 
-    assert_raise ExpectedUrlGeneratiorError do
+    assert_raise NoMethodError do
       @controller.omniauth_authorize_path(:user, :github)
     end
   end