Yes, it has been rename to a more reasonable name - Merge by Distance.
Since Remove Double doesn't explain the operator well by it's own name at all. It merge those vertices which are too closed to each other by the defined distance.
And for developer, API does't change at all. Nothing to worry about it.
In code details
In case someone was interesting in why don't they remove the double by exactly same position?
The problem is the vertices store coordinates (x,y,z, something like that) in float number -- a 32-bit number use in common computer science. It is not always precised in manipulating.
For a easy code in Python 3.6.0:
co = 0.1 # Create a 'co' object that get a float value 0.1
sum_co = 0.0 # Create a 'sum_co ' object that going to store sum
for i in range(10): # Do the block 10 times
sum_co += co # Add co(value: 0.1) to sum_co
sum_co == 1.0 # If sum_co exactly equal to 1.0
# Should be true in common sense since 0.1 * 10 = 1
# But the answer is 'False', the sum_co == 0.9999999999999999
Since this situation happens a lot, Blender can't remove the duplicated vertices by exactly same value of the coordinates. Hence, compared by a tiny tolerance is a more common way to deal with these kind of problem. Therefore, Merge by Distance replaces the original name.