Doc: fix text's description of regexp_replace's arguments.
Section 9.7.3 had a syntax synopsis for regexp_replace()
that was different from Table 9.10's, but still wrong.
Update that one too. Oversight in
580f8727c.
Jian He
Discussion: https://postgr.es/m/CACJufxG3NFKKsh6x4fRLv8h3V-HvN4W5dA=zNKMxsNcDwOKang@mail.gmail.com