In Bank Accounts creation form there are 4 tabs in left hand corner. In 1st tab Account Owner & Use , there is a field to tick Payables, Receivables & Payroll.
Untick Payables. If you have done so then you cant edit this, but in Account Accees tab where you assign this bank account to OUs there is another filed to tick Account Use for Payables. You can untick this because this is not one time editable field.