Revert commenting out "set duration to null"

Author: rfc2822

lib/src/main/kotlin/at/bitfire/synctools/mapping/calendar/AndroidEventProcessor.kt

@@ -147,7 +147,7 @@ class AndroidEventProcessor(
                 if (duration is Duration)
                     duration = Period.ofDays(duration.toDays().toInt())
                 tsEnd = (startDate + duration).toEpochDay() * TimeApiExtensions.MILLIS_PER_DAY
-                //duration = null
+                duration = null
             }
 
             if (tsEnd != null) {
@@ -188,7 +188,7 @@ class AndroidEventProcessor(
                 // Some servers have problems with DURATION, so we always generate DTEND.
                 val zonedStart = dtStartDateTime.toZonedDateTime()
                 tsEnd = (zonedStart + duration).toInstant().toEpochMilli()
-                //duration = null
+                duration = null
             }
 
             if (tsEnd != null) {