DB schema generated by a migration may look different in rails 4 and 5 (because rails 5 may use different default values). For this reason it's important to explicitly set for which rails version a migration was written for. See https://stackoverflow.com/questions/35929869/activerecordmigration-deprecation-warning-asks-for-rails-version-but-im-no/35930912#35930912
These tables, web hooks and services, are unused but where not dropped with the commits d5c91bb9a6 and 2988e1fbf5. The file was left too, but never called.
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