Fix the licensing for shared-mime-info/freedesktop.org.xml to avoid a DMCA takedown

[zRedShift]

So I missed #4 due to some shenanigans with github email notifications, sorry about that.
Yesterday I received a DMCA takedown notice, exactly the same as this gist, so I'm going to adopt the solution since I have very limited time to respond to the notice. I'm not a license lawyer, though.

[pombredanne]

@zRedShift Thanks! Please see also https://gitlab.freedesktop.org/xdg/shared-mime-info/-/issues/154
And I added some more commits that you are welcomed to merge too.
I am NOT behind this and I am as unpleasantly surprised as you are likely BTW.

[zRedShift]

@pombredanne Thanks! I'm well aware that you're not behind the DMCA and were targeted by it as well. I'll merge the newer commits soon.

I haven't touched Go in a while, but I have an experimental project in Rust (on hiatus) for porting this library. There, I opted to use a git submodule for shared-mime-info instead of including the actual files in my repo (mostly for the testing fixtures to ensure the correct behaviour so as not to cause package bloat). It also moves the interaction with the xml file(s) to build time, so that the derivative source code from the parsing (e.g. mediatypes.go in this repo) would not be included in the repo or the package/crate in a package registry. By either providing your own files, or a URL to a shared-mime-info release, it should either avoid any licensing issues completely, or at the very least punt the responsibility of having the correct license to the end-user (in case they pre-compile and redistribute the binaries).

I wonder how to handle the mediatypes.go (et al.) source files In this repository, if our changes aren't enough, and it's necessary to remove the source. Go, AFAIR, doesn't have an explicit build-time, so go generate must be called as part of the go get/vendoring process.

[hadess]

FWIW, I don't think that this is sufficient. You'll need to remove the XML file, or make it clear that the repo is not wholly licensed under the MIT license. That probably still doesn't satisfy the license, but at least it'll be a bit less egregious, and would satisfy my immediate concerns.