I have some PDF/A files that I would like to convert to normal, non-PDF/A, PDF files.
Please note that PDF/A files should be treated as read only, and some interactions (especially with regards to form fields) will no longer work properly if trying to edit. Whether or not the PDF/A file is clearly marked as such.
As for acctually accomplshing what you want, the indicators for PDF/A are in the Metadata entry, but you don't really want to erase that entire entry. Instead you would want to modify it.
To modify, you can extract the XML string, modify using whatever XML tool is handy for you, and then reset. This post shows how to do that.
The three entries are the ones you want to erase.