Revert "Remove exdates from timezone subcomponents because it does not occur there"

This reverts commit 213c3a073e.

src/icalendar/cal.py

@@ -1611,6 +1611,7 @@ class TimezoneStandard(Component):
         vUTCOffset,
     )
     rdates = rdates_property
+    exdates = exdates_property
     rrules = rrules_property
 
 
@@ -1632,6 +1633,7 @@ class TimezoneDaylight(Component):
     TZOFFSETFROM = TimezoneStandard.TZOFFSETFROM
 
     rdates = rdates_property
+    exdates = exdates_property
     rrules = rrules_property
 
 class Alarm(Component):