fixed removing handled header parts from response header

This fix should solve two potential issues:
 1.  ```$this->response = str_ireplace("Transfer-Encoding: chunked\r\n", '', $this->response);``` is able to remove content, also from a response body. To solve this I separate the header from the body first before manipulating the it.
 2. There are pages in the wild which return headers with more than one space between *Transfer-Encoding:* and *chunked*. This fix should solve these issues via regex

I coded this to fix my issue #6689