treewide: use blas and lapack

This makes packages use lapack and blas, which can wrap different
BLAS/LAPACK implementations.

treewide: cleanup from blas/lapack changes

A few issues in the original treewide:

- can’t assume blas64 is a bool
- unused commented code

pkgs/development/libraries/flint/default.nix

@@ -5,11 +5,11 @@
 , mpir
 , mpfr
 , ntl
-, openblas ? null
+, openblas ? null, blas, lapack
 , withBlas ? true
 }:
 
-assert withBlas -> openblas != null;
+assert withBlas -> openblas != null && blas.implementation == "openblas" && lapack.implementation == "openblas";
 
 stdenv.mkDerivation rec {
   pname = "flint";