Remove redundant abs call from Date.Range (#15669)

The preceding clauses handle steps that point away from the last date.
Otherwise, `last_days - first_days` and `step` have the same sign,
so `div/2` is already non-negative.

Author: preciz

lib/elixir/lib/calendar/date_range.ex

@@ -185,7 +185,7 @@ defmodule Date.Range do
            last_in_iso_days: last_days,
            step: step
          }),
-         do: abs(div(last_days - first_days, step)) + 1
+         do: div(last_days - first_days, step) + 1
 
     # TODO: Remove me on v2.0
     defp size(