Further further fix pg_upgrade crossversion test for adminpack.
Apparently, buildfarm animal crake has the adminpack regression DB
named as "regression_adminpack" in some branches. Not clear why
I didn't see that when testing here. In any case, drop that too.
Discussion: https://postgr.es/m/
0CFB76D0-0510-48B2-9916-
1199F93BC28C@yesql.se