Remove duplicate omniauth_only? helper method (#31066)

app/controllers/application_controller.rb

@@ -20,7 +20,6 @@ class ApplicationController < ActionController::Base
   helper_method :current_theme
   helper_method :single_user_mode?
   helper_method :use_seamless_external_login?
-  helper_method :omniauth_only?
   helper_method :sso_account_settings
   helper_method :limited_federation_mode?
   helper_method :body_class_string
@@ -137,10 +136,6 @@ class ApplicationController < ActionController::Base
     Devise.pam_authentication || Devise.ldap_authentication
   end
 
-  def omniauth_only?
-    ENV['OMNIAUTH_ONLY'] == 'true'
-  end
-
   def sso_account_settings
     ENV.fetch('SSO_ACCOUNT_SETTINGS', nil)
   end