bpo-39237, datetime: Remove redundant call to round from delta_new (GH-17877)

diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index c1b2407..0b98cca 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -2489,7 +2489,6 @@
         int x_is_odd;
         PyObject *temp;
 
-        whole_us = round(leftover_us);
         if (fabs(whole_us - leftover_us) == 0.5) {
             /* We're exactly halfway between two integers.  In order
              * to do round-half-to-even, we must determine whether x