upgrade-prep: don't remove boot entry if testing

It's pretty common for me to run the upgrade in test mode, see that
everything is working, and then run it for real. Removing the boot entry
makes that tougher than it needs to be, so leave it alone when we're
testing.
po: update POTFILES.in, add Makefile

I keep forgetting how to regenerate fedup.pot, so here we go.