disable two-factor authentication

See the following from Two-factor authentication for Apple ID - Apple Support regarding turning off two-factor authentication:

If you're already using two-factor authentication with your Apple ID, you can't turn it off. If you updated to two-factor authentication inadvertently, you can turn it off within two weeks of enrollment. If you do, your account is less secure and you can't use features that require a higher level of security.

This discussion offers more detail, but basically, you cannot turn off this safety feature.