ghostty: remove adjust-cell-width

At some point, I updated ghostty and this became unnecessary, making
fonts look weird. It's possible I only originally needed it because of a
bug of some kind.

nix/home-manager/ghostty.nix

···
     font-family = "Hack";
     font-size = 12;
     font-thicken = true;
-    adjust-cell-width = -1;
 
     window-padding-color = "background";
     window-padding-x = 3;