Your wrapper does do a bunch of extra things that aren't necessary, but pulling in a library here is a far greater maintenance and security liability than writing those 100 lines of trivial code for the umpteenth time.

So yes you should just write and keep those lines. The fact that you haven't touched that file in 3 years is a great anecdotal indicator of how little maintenance such a wrapper requires, and so the primary reason for using a library is non-existent. Not like the fetch API changes in any notable way, nor does the needs of the app making API calls, and as long as the wrapper is slim it won't get in the way of an app changing its demands of fetch.

Now, if we were dealing with constantly changing lines, several hundred or even thousand lines, etc., then it would be a different story.

But you said so yourself they are necessary… otherwise you would just use fetch. This reasoning is going around in circles.