Remove sum_over_features from sklearn.metrics.manhattan_distances #24597
Description
sklearn.metrics.manhattan_distances with sum_over_features=False does not return distances, looks unused, and is also unlikely used by users.
I think the behavior for sum_over_features=True should be the unique one for manhattan_distances; in this case, sum_over_features would be removed this from the public API after a deprecation cycle.
This was first discussed in #23958 (comment).