Move scripts to Nix files

Move the scripts I commonly use into Nix files managed by Home Manager.

Some, like `mounter` and `unmounter` are desktop-only, but this can be
addressed in a future commit to create per-host scripts or
desktop/non-desktop scripts.

This commit also removes a number of unused scripts that are either
included in packages like `git-extras` or aren't used.

modules/home-manager/cli/scripts/setbg.nix

@@ -0,0 +1,11 @@
+{ pkgs, writeShellApplication }:
+
+writeShellApplication {
+  name = "setbg";
+
+  runtimeInputs = with pkgs; [ xwallpaper ];
+
+  text = ''
+    xwallpaper --zoom "''${XDG_REPOS_DIR}/personal/nix-config/wallpaper/wallpaper.jpg"
+  '';
+}