More cleanup of a2ab9c06ea.

More cleanup of a2ab9c06ea.

Require SELECT privileges when performing UPDATE or DELETE, to be
consistent with the way a normal UPDATE or DELETE command works.

Simplify subscription test it so that it runs faster. Also, wait for
initial table sync to complete to avoid intermittent failures.

Minor doc fixup.

Discussion: https://postgr.es/m/CAA4eK1L3-qAtLO4sNGaNhzcyRi_Ufmh2YPPnUjkROBK0tN%3Dx%3Dg%40mail.gmail.com
Discussion: https://postgr.es/m/1514479.1641664638%40sss.pgh.pa.us
Discussion: https://postgr.es/m/Ydkfj5IsZg7mQR0g@paquier.xyz