Revert async process substitution & completion strategy

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

src/features.zsh

@@ -0,0 +1,19 @@
+
+#--------------------------------------------------------------------#
+# Feature Detection                                                  #
+#--------------------------------------------------------------------#
+
+_zsh_autosuggest_feature_detect_zpty_returns_fd() {
+	typeset -g _ZSH_AUTOSUGGEST_ZPTY_RETURNS_FD
+	typeset -h REPLY
+
+	zpty zsh_autosuggest_feature_detect '{ zshexit() { kill -KILL $$; sleep 1 } }'
+
+	if (( REPLY )); then
+		_ZSH_AUTOSUGGEST_ZPTY_RETURNS_FD=1
+	else
+		_ZSH_AUTOSUGGEST_ZPTY_RETURNS_FD=0
+	fi
+
+	zpty -d zsh_autosuggest_feature_detect
+}