Fix comments related to table AMs
Incorrect function names were referenced. As this fixes some portions
of tableam.h, that is mentioned in the docs as something to look at when
implementing a table AM, backpatch down to 12 where this has been
introduced.
Author: Hironobu Suzuki
Discussion: https://postgr.es/m/
8fe6d672-28dd-3f1d-7aed-
ac2f6d599d3f@interdb.jp
Backpatch-through: 12