Dropping more libraries

[PallHaraldsson]

MPFR_jll (and more) does not seem "obligatory". If it is then it seems easily fixed. I'm reviewing the code, and e.g. openlibm seems droppable (soon, if not already).

I was under the illusion you can drop libraries, until I noticed the exceptions.

SuiteSparse and all it entails, should go by default if not already, since GPL (and opt-in to include it, or would happen automatically if you add to your Projects.toml file?). I believe it's only bundled now in Julia (next release, at least).