Commit 05c8482f added special logic related to parallel-safety of FK
triggers. This is a bit of a hack and should have instead been done by
simply setting appropriate proparallel values on those trigger functions
themselves.

Suggested-by: Tom Lane
Author: Greg Nancarrow
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/2309260.1615485644@sss.pgh.pa.us