How to remove symbols (pairs) from the market watch for good?

I think hide is the same as delete though for this. I just checked and when you right-click on a symbol it says hide and delete on the same line. So the same option performs the either action. Either hide or delete or whatever you want to call it.

It seems you want to permanently remove a symbol without there ever being a choice to add it later again if you change your mind. In this case, I do not think it's possible since this isn't how MT4 was designed to work.

Like you said - selected pair is still on the  market watch list as hidden but not permanently deleted.

If you hide/delete the selected symbol, it doesn't appear in the market watch anymore though. I just tested it and it worked. The symbol removes completely from the list and then it won't appear again in the list until it is intentionally added again. So I'm not sure what you mean.

I am curious why you want to be able to permanently delete a symbol from the platform though?