Rewrite Deadcode::Reference as a bare Ruby class

Signed-off-by: Alexandre Terrasa <alexandre.terrasa@shopify.com>

Author: Morriar

lib/spoom/model/reference.rb

@@ -7,7 +7,7 @@ class Model
     #
     # Constants could be classes, modules, or actual constants.
     # Methods could be accessors, instance or class methods, aliases, etc.
-    class Reference < T::Struct
+    class Reference
       class Kind < T::Enum
         enums do
           Constant = new("constant")
@@ -27,9 +27,21 @@ def method(name, location)
         end
       end
 
-      const :kind, Kind
-      const :name, String
-      const :location, Spoom::Location
+      #: Kind
+      attr_reader :kind
+
+      #: String
+      attr_reader :name
+
+      #: Spoom::Location
+      attr_reader :location
+
+      #: (kind: Kind, name: String, location: Spoom::Location) -> void
+      def initialize(kind:, name:, location:)
+        @kind = kind
+        @name = name
+        @location = location
+      end
 
       #: -> bool
       def constant?