The "built-in" way to look for Input Validation formulas is to run a Design Synopsis on all Forms and Subforms in a database, and do a search on "Input Validation Formula" for the resulting document.
You could also use a DXL export to search. I don't have any code that specifically looks for Input Validation formulas, but it could be written.
In terms of removing the existing fields, you could technically do that with DXL, but it might be a little risky. I'd probably recommend a manual effort for that.