Account for header type when removing headers

[MihaZupan]

Fixes #1334

Unlike TryAddWithoutValidation, HttpHeaders.Remove will throw if the header name does not belong to the header collection type.

As a result, trying to remove foo from content headers or trying to remove Content-Encoding from request headers will result in an exception.

Instead of trying to remove the header from both collections, we should check which collection the header belongs to first.