Without being able to look under the hood and see what it connects to on the other end, it appears to be part of the heater system.
If you are planning to replace that pipe then my honest answer to how to get it out is, any which way you can. Ok that's not really my honest answer that's more me being a smart butt. 🙃 For pipes like this that are sealed with an o-ring what I like to do is grab the pipe with a pair of pliers and wiggle it back and forth gently until the pipe begins to rotate. Then it's usually as simple as pulling it out in the correct direction. Sometimes that's by hand sometimes it's using the pliers. Sometimes the pliers aren't necessary to get the pipe rotating at all. Sometimes you can put a flat head screw driver behind the flange that's for the bolt and twist and that will gently pull the pipe out of the hole. Hope that helps.
