opam: remove aspcud from runtime

[ylh]

Description of changes

see title (& appeased a strictness warning in opam.nix.pl); motivation:

• per opam docs:
  • external solvers have not been the default recommendation since 1.2.2
  • opam will detect supported solvers at runtime for those with (what are now considered) niche use cases
• drop a transitive build dependency on scons
  • scons in particular has been a common factor amongst breakages following an otherwise innocuous adjustment to cc-wrapper (cc-wrapper: broaden explicit libc++abi linking for LLVM stdenv #181485)
  • minimise ocaml's risk exposure to python ecosystem volatility

result of nixpkgs-review --rev HEAD:

2 packages built:
dune-release opam

cursory test drive shows that opam still resolves dependencies perfectly competently

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 22.11 Release Notes (or backporting 22.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[henrytill]

👍 LGTM