Remove unused JoinPart#name

Author: kamipo

activerecord/lib/active_record/associations/join_dependency/join_part.rb

@@ -22,10 +22,6 @@ def initialize(base_klass, children)
           @children = children
         end
 
-        def name
-          reflection.name
-        end
-
         def match?(other)
           self.class == other.class
         end