Remove vendored dependencies

[traversaro]

osqp contains some vendored dependencies (qdldl and amd from suitesparse) that it would be a good idea to remove and use proper recipes instead to avoid tricky ABI issues in the future. From the discussion in osqp/osqp#85 it may be necessary to still use the vendored qdldl and amd for code generation, but as code generation is something only available at high level (Python and MATLAB) we can see how to deal with it at the osqp-feedstock level, that mantains the osqp Python bindings.

[traversaro]

This is related to conda-forge/scs-feedstock#18 as well, given that scs vendors exactly the same dependencies (qdldl and amd from suitesparse).

[h-vetinari]

With #8 we have now gotten rid of qdldl at least. The suitesparse bits would be nice to get rid of as well, but they seem to be really old (2015 judging by the license, though at least 2018; haven't dug back further in the git history), so I'm not sure if they're drop-in recompilable with a current suitesparse.