zsh: Explicitly disable prompt in user config

Otherwise starship does not work in 21.05.

users/simon/modules/zsh.nix

@@ -64,7 +64,11 @@ in
       envExtra = ''
         export _JAVA_OPTIONS="-Dawt.useSystemAAFontSettings=on"
       '';
-      initExtra = lib.mkAfter ''
+      initExtra = lib.mkMerge [
+        (lib.mkBefore ''
+          prompt off # collides with starship
+        '')
+        (lib.mkAfter ''
           eval $(${pkgs.coreutils}/bin/dircolors -b ${dircolors-solarized}/dircolors.ansi-universal)
 
           # no sad smiley (starship shows exit status)
@@ -74,7 +78,8 @@ in
           disable -p '#'
 
           source ${../files/zsh/pass-wrappers.zsh}
-      '';
+        '')
+      ];
     };
   };
 }