pkg keeps wanting to install python27 but nothing uses it

[Mel Pilgrim]

My systems have the public FreeBSD pkg repo disabled and instead install 
from a local repo built using poudriere.  The current repo, built from 
branch 2019Q3 r506787, doesn't have a python27 pkg in it because 
everything uses python36.

On a few systems (e.g., the poudriere build server), I must have the 
stock FreeBSD repo enabled.  There, pkg insists on installing python27 
from the FreeBSD repo.  If I run pkg-autoremove afterward, it gets 
deleted, yielding an endless loop of pkg-upgrade insisting python27 
needs to be installed, and pkg-autoremove insisting it doesn't.

The usual incantation of:

# pkg clean -a
# pkg update -f
# pkg upgrade -f

didn't fix it.  Why is pkg insisting I have python27 installed?