Per the docs, to turn off geolocation:

mixpanel.setUseIpAddressForGeolocation(false);

This sets the useIpAddressForGeolocation setting, which is later read to set the ?ip=(0|1) querystring param.

However, the getter has a bug where it always returns true:

https://github.com/mixpanel/mixpanel-react-native/blob/master/javascript/mixpanel-config.js#L67-L72