fasd: use xdg-open in o alias back again

Fixes #6314

plugins/fasd/fasd.plugin.zsh

@@ -7,6 +7,6 @@ if [ $commands[fasd] ]; then # check if fasd is installed
   unset fasd_cache
 
   alias v="f -e \"$EDITOR\""
-  alias o='a -e open_command'
+  alias o='a -e xdg-open'
   alias j='zz'
 fi