Remove duplicated code (apparently introduced by commit c8ea87e4).
Also get rid of some PG_USED_FOR_ASSERTS_ONLY variables we don't
really need to have.

Li Japin, Tom Lane

Discussion: https://postgr.es/m/PS1PR0601MB3770A5595B6E5E3FD6F35724B6360@PS1PR0601MB3770.apcprd06.prod.outlook.com