You can also remove it in Foxit PhantomPDF - it is much better then Acrobat: fast, less weight, it remembers last opened page for any pdf (Acrobat doesn't remember it for any pdf file, only some)
How to remove PDF "A" infomation in "Foxit PhantomPDF":
- open file in PhantomPDF
- click on "convert"
- click on "industry standart"
- check "PDF/A comliance"
- double click "remove PDF/A inforamtion"
- save new file