Mention of PG 14 in docs

In patch "Handle equality operator in contrib/pg_trgm" (935f66665), I
see this text:

-->	<literal>~</literal> and <literal>~*</literal> queries.  Beginning in
-->	<productname>PostgreSQL</productname> 14, these indexes also support
	equality operator (simple comparison operators are not supported).
	Note that those indexes may not be as efficient as regular B-tree indexes
	for equality operator.

As far as I know, we don't usually mention what version _added_ a
feature like this.  I suggest the PG 14 mention be removed.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  If only the physical world exists, free will is an illusion.