In Days of Future Past (2014), Wolverine erases the old timeline and starts a new one.
Which X-Men films' timelines were erased?
Please no spoilers.
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Per Writer and Producer Simon Kinberg, "erased" is not an accurate description of how the timelines have been affected. As such, it is only a matter of opinion to state which aspects of the various films may no longer be relevant to timelines moving forward from DOFP.
“The end of Days of Future Past in 1973 does change the timeline of the established film universe. But one of the things we posit in the film is the immutability of time. So what you see at the end is a future that has been shifted but not completely transformed. Our characters are back in the mansion, as we saw them in X1-3, with some obvious changes (like certain characters being alive). So the answer is yes and no. Yes it changes the timeline. No it doesn’t completely erase everything…”
“Characters can change, but, like time, they are on a general path that cannot be completely undone.”
-- Simon Kinberg
Unlike, for example Back To The Future (1985) where time travel to the past can literally erase things from the future, the immutable timeline which Kinberg posits may shift the details of the timeline without erasing anything.