Don't free extra, the GUC machinery doesn't like it

Without free:

	ams=# show pgaudit.log;
		pgaudit.log
	-------------------
	 read, write, user
	(1 row)

With free:

	ams=# show pgaudit.log;
	 pgaudit.log
	-------------
	 \x0B+
	(1 row)

I don't know why it happens, but I know which version I prefer.