In accordance with T56648, this changes the name of the Remove Doubles operator to Merge by Distance. This patch only changes the user-visible name, not the Python API.
Why the name change?
The current Remove Doubles operator name is not clear: 'Doubles' implies exactly two items, even though it works in an arbitrary number of vertices. 'Remove' is also misleading - really it's just performing a merge operation.
Since this operator is really just a special kind of Merge that takes distance into account, the name can reflect that.
Alternative options: Distance Merge, Proximity Merge