Doc: adjust misleading phrasing of a few cross-references.

Doc: adjust misleading phrasing of a few cross-references.

The pg_dump and pg_dumpall man pages referred to app-psql-patterns
as appearing "below", which I suspect was copied-and-pasted from
equivalent text in psql-ref.sgml rather than being actually thought
through.  At least to me, that phrasing means "later in this same
web page/section", which this link target is not.  Drop the
misleading and unnecessary-in-any-case adjective.