tests: remove SKIP_CLOUDFLARE_CHECK env variable.

This was a hack to deal with the Cloudflare check sometimes being slow
or timing out during tests. The call to https://api.cloudflare.com/client/v4/ips
could hang if there were IPv6 connectivity problems. If this happens, make
sure that IPv6 is configured properly and that `curl -v --http1.1 -6 https://api.cloudflare.com/client/v4/ips`
works.

app/logical/downloads/file.rb

@@ -92,8 +92,6 @@ module Downloads
     end
 
     def is_cloudflare?(url)
-      return false if ENV["SKIP_CLOUDFLARE_CHECK"]
-
       ip_addr = IPAddr.new(Resolv.getaddress(url.hostname))
       CloudflareService.new.ips.any? { |subnet| subnet.include?(ip_addr) }
     end