chore: Drop unused packages

I only used inkscape to convert svg to png with the following command:
`fd -e svg -x inkscape -w 512 -h 512 "{}" -o "{.}.png"`

gthumb was crashing and I'd rather not have to deal with a non-trivial
GUI program that crashes on launch.

nb and obsidian are cute but ultimately I found quartz to be better for
my use case.

modules/packages.nix

@@ -21,7 +21,6 @@
     sqlcipher
     kanjidraw
     libreoffice
-    inkscape
     krita
     aegisub
     element-desktop
@@ -50,7 +49,6 @@
     brightnessctl
     zellij
     hexyl
-    nb
     jpegoptim
     playerctl
     recode
@@ -122,8 +120,6 @@
     mgitstatus
     pnpm-shell-completion
     rclone
-    obsidian
-    gthumb
   ];
 
   nixpkgs.config.allowUnfree = true;