devshell: remove unneeded PS1_util

It's already present in upstream:
67cce7359e/modules/devshell.nix (L425-L441)

tritonshell.nix

@@ -11,23 +11,6 @@ in
   name = "tritonshell";
 
   devshell.interactive = {
-    PS1_util = pkgs.lib.noDepEntry ''
-      if [[ -n "''${PRJ_ROOT:-}" ]]; then
-        # Print the path relative to $PRJ_ROOT
-        rel_root() {
-          local path
-          path=$(${pkgs.coreutils}/bin/realpath --relative-to "$PRJ_ROOT" "$PWD")
-          if [[ $path != . ]]; then
-            echo " $path "
-          fi
-        }
-      else
-        # If PRJ_ROOT is unset, print only the current directory name
-        rel_root() {
-          echo " \W "
-        }
-      fi
-    '';
     PS1.text = ''
       PS1='\[\033[38;5;202m\][$SDC_ACCOUNT@$TRITON_DC]$(rel_root)\$ \[\033[0m\]'
     '';