Previously if a user attempted to click on a link to an attachment for a
renamed project (e.g. https://gitlab-org/gitlab-ce/uploads/123.png),
Rails would redirect the user to an erroneous URL
(e.g. https://gitlab-org/gitlab-foss/uploads/123.png.png). Notice the
redirect URL contains a redundant extension.

It turns out Rails 5 parses the extension of a route as the format
(https://github.com/rails/rails/issues/28901#issuecomment-297747521),
and the URL generator appends the format to the redirected route.

To fix this, we need to disable the format path parameter and explicitly
set the format to `nil`. If we do not set the format to `nil`, the URL
generator will append a query string (e.g `?format=png`), which would
still work but not necessary.

Closes https://gitlab.com/gitlab-org/gitlab/issues/196232