Emacs is really trying to help you here. Read the info page on Protection against Simultaneous Editing.
But, if you still want to avoid that message/prompt, you can redefine the function that is doing the prompting:
(defun ask-user-about-supersession-threat (fn) "blatantly ignore files that changed on disk" ) (defun ask-user-about-lock (file opponent) "always grab lock" t)
The second function there is for when two people are using Emacs to edit the same file, and would provide a similar prompt (but not the one you seemed to refer to in the question).
I’d advise against overriding the two routines, but it’s there if you want.
On the off chance
global-auto-revert-mode is on, you could disable that. Add this to your .emacs:
You can tell if the mode is on by looking at the variable of the same name:
C-h v global-auto-revert-mode RET
If the value is
t, then the mode is on, otherwise it is off.