Update nix and use an overlay

[saschagrunert]

This will:

• Fix and run make nixpkgs to update the dependencies
• Reduce duplication by using overlay.nix
• Pushed manually to cachix to refresh the build cache
• Switched to pcre2 instead of pcre
• Removed static.nix, since it's not required any more

All CI binaries look sane:

> file *
conmon_0: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, for GNU/Linux 3.10.0, stripped
conmon_1: ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), statically linked, for GNU/Linux 3.10.0, stripped
conmon_2: ELF 64-bit LSB executable, 64-bit PowerPC or cisco 7500, OpenPOWER ELF V2 ABI, version 1 (SYSV), statically linked, for GNU/Linux 3.10.0, stripped
conmon_3: ELF 64-bit LSB executable, UCB RISC-V, RVC, double-float ABI, version 1 (SYSV), statically linked, for GNU/Linux 4.15.0, stripped