The call recording alert feature cannot be turned off. As the device works with Google's communication suite, due to privacy regulations/local laws, the Google team is required by law to add this feature by default.
But you can turn on the Play audio tone instead of the disclaimer and replace the audio notification with an audio tone (beep). However, if you choose to use the audio tone, you agree to comply with all laws and requirements related to recording phone conversations, including the privacy rights of the individuals involved, and that Google will not be responsible for any violation of law resulting from your actions.
Path: Phone > 3 dots on the top right > Settings > Call recording > Play audio tone instead of disclaimer.