meta: Drop default hardware

From a pragmatic perspective this never made sense since it would be
unlikely that we'd ever want to import multiple hardware configurations
at the same time.

An alternative solution would be to let users generate their own
hardware-configuration.nix that they can use with this nix-config, or
simply have them create their own nix-config that imports this flake and
uses the outputs they want.

hardware/default.nix

@@ -1,5 +0,0 @@
-{
-  imports = [
-    ./laptop.nix
-  ];
-}