update verbiage to be more concise

config/locales/en.yml

@@ -12,7 +12,7 @@ en:
 
   devise:
     failure:
-      no_authentication_allowed: 'You are attempting to access a resource as an authenticated user when that is not allowed. Please sign out and try again.'
+      already_authenticated: 'You are already signed in.'
       unauthenticated: 'You need to sign in or sign up before continuing.'
       unconfirmed: 'You have to confirm your account before continuing.'
       locked: 'Your account is locked.'

lib/devise/controllers/internal_helpers.rb

@@ -114,7 +114,7 @@ MESSAGE
       def require_no_authentication
         if warden.authenticated?(resource_name)
           resource = warden.user(resource_name)
-          flash[:alert] = I18n.t("devise.failure.no_authentication_allowed")
+          flash[:alert] = I18n.t("devise.failure.already_authenticated")
           redirect_to after_sign_in_path_for(resource)
         end
       end

test/controllers/internal_helpers_test.rb

@@ -50,7 +50,7 @@ class HelpersTest < ActionController::TestCase
     @mock_warden.expects(:user).with(:user).returns(User.new)
     @controller.expects(:redirect_to).with(root_path)
     @controller.send :require_no_authentication
-    assert flash[:alert] == I18n.t("devise.failure.no_authentication_allowed")
+    assert flash[:alert] == I18n.t("devise.failure.already_authenticated")
   end
 
   test 'signed in resource returns signed in resource for current scope' do