While whitelisting wallets to withdraw to is not a mandatory procedure, we strongly encourage it as an an additional security measure.
To disable the withdrawal whitelist select the Withdrawal Whitelist option from the drop down menu under your account name.
On this page in the upper right there are a couple buttons in the upper right, one of which says Disable Withdrawal Whitelist.
Clicking on the Disable Withdrawal Whitelist button will bring up a dialog box that asks you to confirm that you wish to disable withdrawal whitelisting. If you have 2FA authentication enabled you will also be asked to enter a 2FA code.
When you confirm your decision by clicking on the Disable button, you will get a confirmation message.