No need to check for :uniq

[#5170 state:resolved]

Signed-off-by: José Valim <jose.valim@gmail.com>

activerecord/lib/active_record/associations/association_collection.rb

@@ -478,13 +478,10 @@ def add_record_to_target_with_callbacks(record)
           callback(:before_add, record)
           yield(record) if block_given?
           @target ||= [] unless loaded?
-          index = @target.index(record)
-          unless @reflection.options[:uniq] && index
-            if index
-              @target[index] = record
-            else
+          if index = @target.index(record)
+            @target[index] = record
+          else
              @target << record
-            end
           end
           callback(:after_add, record)
           set_inverse_instance(record, @owner)