I have a Samsung Galaxy S5. How do you permanently turn off the wifi?

[AC Question]

I do not want my phone to be able to connect to any wifi anywhere but I want to be able to text and talk. I have a Samsung Galaxy S5 phone. My phone company has already turned off my data but the wifi still connects to the internet. I know I can get a basic flip phone but then it will be difficult to do texting on a basic phone. Also I want to be able to control when the wifi is turned on or off. I do not want the person who may use my phone to be able to turn it on or off. How can I lock the access to the wifi if it cannot be removed or permanently deactivated? I saw a response on the internet a few months ago but I can't find it now. Someone said that you can remove the application that connects to the wifi. If you can tell me how to do that it would be greatly appreciated.