Remove remaining mentions of BDbags

[kltm]

Noting that, apparently, no BDBag manifest has been created since 2022-01-13. I no longer recall if we were getting rid of both or just the reference ones--or whether, in fact, there was more than one in the first place---but as a practical matter, we have not for some time to no complaint, so we should probably remove the remaining mentions of it.

Tagging @suzialeksander