Remove deprecated namespaced_key

activesupport/lib/active_support/cache.rb

@@ -549,14 +549,6 @@ def normalize_key(key, options)
           key
         end
 
-        def namespaced_key(*args)
-          ActiveSupport::Deprecation.warn(<<-MESSAGE.strip_heredoc)
-            `namespaced_key` is deprecated and will be removed from Rails 5.1.
-            Please use `normalize_key` which will return a fully resolved key.
-          MESSAGE
-          normalize_key(*args)
-        end
-
         def instrument(operation, key, options = nil)
           log { "Cache #{operation}: #{normalize_key(key, options)}#{options.blank? ? "" : " (#{options.inspect})"}" }
 

activesupport/test/caching_test.rb

@@ -566,12 +566,6 @@ def test_cache_miss_instrumentation
   ensure
     ActiveSupport::Notifications.unsubscribe "cache_read.active_support"
   end
-
-  def test_can_call_deprecated_namesaced_key
-    assert_deprecated "`namespaced_key` is deprecated" do
-      @cache.send(:namespaced_key, 111, {})
-    end
-  end
 end
 
 # https://rails.lighthouseapp.com/projects/8994/tickets/6225-memcachestore-cant-deal-with-umlauts-and-special-characters