Don't use Roda's streaming plugin in download_endpoint
Don't use Roda's streaming plugin in download_endpoint

Roda 3 will remove EventMachine support, making the streaming plugin
essentially only syntactic sugar for what we can already achieve with
Rack::BodyProxy. I don't know for which web server was rack.async even
useful, because Thin already uses EM.defer when returning the response.

This makes download_endpoint load less code (as Rack::BodyProxy is
already loaded by other parts of Rack), so it uses less memory.

janko-m/shrine,janko-m/shrine