The Short Answer:
Prior to disabling Personal Vault, make sure you've moved or copied any files you want to keep from the Personal Vault folder to another location
Go to the OneDrive website
, which you can access by tapping the View Online button on the OneDrive system tray icon
Navigate to Options -> Personal Vault (which, at the time this post was written, could be reached by going here
Where you see the Disable Personal Vault option, tap Disable, then confirm you want to remove the personal vault folder and all files it contains
I use OneDrive for several purposes. One is for offsite backup of some files that automatically get copied to a OneDrive folder. This process happens on a computer that I don't use very often in-person, and where I would very rarely want to unlock my Personal Vault.
However, OneDrive has a terrible bug where it won't complete a sync unless Personal Vault is unlocked. So, whenever I do visit this particular computer, my OneDrive system tray icon has an error icon, and I find that I have dozens of errors all telling me that sync failed because my Personal Vault was locked.
Of course it was locked! That's the whole point... I want it to be locked on that computer. But the OneDrive team once again failed to anticipate how their product is actually used. Rather than sync everything other than Personal Vault, they just bring the whole thing to a halt.
So, Personal Vault is not a feature I'll be using anymore. And I had a hard time figuring out how to disable it, since it doesn't seem to show up in local settings, and I think of the OneDrive website as an in-case-of-emergency approach to accessing files that I typically just open from the file system of one of my laptops... so it took me a while to think to look there for the master switch.
Hope this helps!