Is it possible to destroy a village?

You need to do the following:

• Destroy all bells (not sure about this one)
• Destroy all beds
• Destroy all doors (if below 1.14)
• Destroy the buildings that give villagers their jobs, e.g. a masonry (this took me a while to figure out)
• Kill all villagers (not sure about this one)

In 1.14 the Village mechanics got reworked, and the definition of a Village is the following:

A village needs at least one house and at least one villager in order to be a "village". A "house" is a bed.

https://minecraft.gamepedia.com/Village/Mechanics#House

In older versions:

A village needs at least one house and at least one villager in order to be a "village". A "house" is defined simply as a wooden door with an "inside" and an "outside".

https://minecraft.gamepedia.com/Tutorials/Legacy_Console_village_mechanics#Terminology

If you've destroyed everything (including the Villagers), then the game should consider the village non-existent, and therefore it shouldn't interfere with your contraptions.

My first tip is make sure there are absolutely no villagers alive, and there is no proof that a village existed, ie., not a single piece of wood. As @Andruida mentioned, a village needs at least one house and villager to be functioning.

After that, I don't think it's a good idea to copy Mumbo, because he didn't make a tutorial video so he didn't explain everything, and so he might've changed some stuff of camera or you missed this one tiny block. He put a link to the tutorial he followed, so you can check that out if you want to build you're own iron farm.