I started to write about what trans people call their deadnames, in the wake of the announcement by Elliot Page, but it got longer than I have any right to impose. I speak here purely as a cis person who wants to be supportive of trans people, and who is also concerned with clarity and informativeness.
Summarizing then: I think that most trans people, and anybody else whose name was changed before (if ever) they became famous, should have the right to suppress their deadnames if they choose.
But cases like Page who already had public careers under that name are in a different status. We can learn to use the new name exclusively; we've done that before. Yet the old name is still out there; it can be changed retroactively online and in new releases, but it can't be erased universally and new people coming across Page's old work will need to be informed who's who and what's what, to avoid inadvertent errors. So in these cases, the deadname should be included in the person's entry in reference sources like Wikipedia, but it doesn't need to be in boldface in the first paragraph.
Incidentally, this shoe fits on the other foot as well. John Oliver may think it funny to call Donald Trump "Donald Drumpf", but that's a deadname that was abandoned by his grandfather if not two centuries earlier, and we shouldn't use it any more than we should deny that Elliot Page is male.