Prefer extend self over module_function, feedback:

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5620#note_13672004
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5620#note_13810498

lib/gitlab/data_builder/build_data_builder.rb

 module Gitlab
   module DataBuilder
     module BuildDataBuilder
-      module_function
+      extend self
       def build(build)
         project = build.project

lib/gitlab/data_builder/note_data_builder.rb

 module Gitlab
   module DataBuilder
     module NoteDataBuilder
-      module_function
+      extend self
       # Produce a hash of post-receive data
       #

lib/gitlab/data_builder/pipeline_data_builder.rb

 module Gitlab
   module DataBuilder
     module PipelineDataBuilder
-      module_function
+      extend self
       def build(pipeline)
         {

lib/gitlab/data_builder/push_data_builder.rb

 module Gitlab
   module DataBuilder
     module PushDataBuilder
-      module_function
+      extend self
       # Produce a hash of post-receive data
       #