Remove FUNDING.yml

I don't really do enough on this project anymore to justify having
the sponsor button include me. I can cover the server costs fine,
and I feel uncomfortable asking for money. It in fact has caused
some stress for me as I feel bad whenever I think about overviewer
because I know there's so much code rot and big stuff that needs
to be done but I'd rather spend my time on different projects, and
when I'm asking for money it builds the expectation that I will
actually eventually get around to doing all those things, which
I realistically won't be.

Sorry for disappointing, I think it's better this way for both me
and the Overviewer community.

Author: CounterPillow