docs: remove TODO note, write a comment on the PR

shell/completion.zsh

@@ -307,10 +307,9 @@ fzf-completion() {
   local tokens prefix trigger tail matches lbuf d_cmds
   setopt localoptions noshwordsplit noksh_arrays noposixbuiltins
 
-  # TODO: To successfully complete 'test_dir_completion', add an explanation!
-  # It has to do with the presence of 'zle -C …' 
-  if ! zmodload -Fe zsh/{complete,compctl}; then
-    zmodload -i zsh/{complete,compctl}
+  # Check if at least one completion system (old or new) is active
+  if ! zmodload -e zsh/compctl || ! (( $+functions[compdef] )); then
+    zmodload -i zsh/compctl
   fi
   # http://zsh.sourceforge.net/FAQ/zshfaq03.html
   # http://zsh.sourceforge.net/Doc/Release/Expansion.html#Parameter-Expansion-Flags