Turning off the tax feature or switching to the old tax is irreversible in QuickBooks. As a workaround, you can change the default tax rate to No VAT. Once you create a transaction, you will no longer be prompted to enter a VAT code.
Go to the Gear icon.
Choose the Account and Settings button.
Click the Advanced tab, then hit Accounting.
In the Default tax rate selection drop-down, select No VAT.
Tap Save, then Done.
I've attached an article about managing taxes and other related topics.