Old villagers that had custom trades now have a bunch of vanilla trades included in their tables

Partner Rank: 3

Verification builds: Beta 1.12.0.4 release 2160393

Summary: Old villagers that had custom trades now have a bunch of vanilla trades included in their tables

Impact: Bad player experience and impossible for a partner to fix because in the new villagers we're unable to make the same trades available for the player so it would break the map.

Repro Steps:

1. Download Play: City Mall from the marketplace
2. open the trade window on the nearby villager
3. Scroll to the end of their available trades

Observed Results: Vanilla trades will show up at the end of their pre-set trades

 Expected Results: Only the trades set on them should be available as in all previous versions. in This example, it should stop at the emerald trades and not include a trade for a map like this.

Screenshots/Videos attached:    

Regression builds: 1.11