treewide: libressl.nc -> netcat

Quote from NixOS 25.11 release notes:

> `meta.mainProgram` is now used to determine the `NIX_MAIN_PROGRAM` environment variable. This means that changing it can now lead to a package rebuild.

And `netcat` is:

```
 netcat = libressl.nc.overrideAttrs (old: { 
   meta = old.meta // { 
     description = "Utility which reads and writes data across network connections — LibreSSL implementation"; 
     mainProgram = "nc"; 
   }; 
 });
```

`netcat` and `libressl.nc` are 2 different derivations now, use just one
 of them in nixpkgs for consistency.

This also fixes lots of warnings if `virtualisation.libvirtd.enable = true`:

```
pkgs.buildEnv warning: colliding subpath (ignored): `/nix/store/1mcayh9rmxmjcbmm6swkkyr59rjl66vc-libressl-4.2.1-nc/bin/nc' and `/nix/store/x1vmfpisbd494yykmvjkhvh3dplsnjhg-libressl-4.2.1-nc/bin/nc'
...
```

0 files changed, 0 insertions, 0 deletions