Do not use "Transfer-Encoding: chunked" header for proxied DELETE requests (again)

[Turbo87]

This issue is related to PR #373 where this exact bug was already fixed by a89e2f2, but then later apparently introduced again by 8663ac1.

The actual problem is that DELETE requests with both Content-Length: 0 and Transfer-Encoding: chunked are illegal and are being rejected by some servers (in this case nodejs since v0.10.42). If the incoming request only has the Transfer-Encoding header the proxy will somehow automatically set the Content-Length header to 0 but won't remove the encoding header which leads to this issue.

[jcrugzz]

@Turbo87 looks like this was lost in translation when the rewrite happened. I'd love PR for this 👍. Definitely a good first contributor issue :)