Revert async process substitution & completion strategy

They're not quite ready. Keep them on a feature branch for now.

src/config.zsh

@@ -69,5 +69,5 @@
 # Max size of buffer to trigger autosuggestion. Leave null for no upper bound.
 : ${ZSH_AUTOSUGGEST_BUFFER_MAX_SIZE=}
 
-# Pty name for capturing completions for completion suggestion strategy
-: ${ZSH_AUTOSUGGEST_COMPLETIONS_PTY_NAME=zsh_autosuggest_completion_pty}
+# Pty name for calculating autosuggestions asynchronously
+: ${ZSH_AUTOSUGGEST_ASYNC_PTY_NAME=zsh_autosuggest_pty}