Hi Guix!

I realized today that a new version of crypto++ was out so I set out to
update it but Clementine failed to compile. There's a patch on master [0]
that fixes the issue so I was going to apply it when I realized the bit
of code in question downloads a binary blob to support Spotify.  It
turns out there's a button in the preference menu that allows users to
download this proprietary blob, and crypto++ appears to be used to check
it.

So I thought that rather than apply the patch, we should probably remove
support for this download button all together. There is a flag that
allows not compiling "spotifyblobdownloader.cpp".

Also, this was also the only place in the codebase that used crypto++ so
we can drop this input.

What do you think?

[0]: https://github.com/clementine-player/Clementine/commit/38c1f8777cecc7b2f91fecbcc48c41479839304b.patch