Revert "First steps into pytz deprecation"

This reverts commit e4e7d50659.

src/pretix/base/reldate.py

@@ -22,8 +22,8 @@
 import datetime
 from collections import namedtuple
 from typing import Union
-from zoneinfo import ZoneInfo
 
+import pytz
 from dateutil import parser
 from django import forms
 from django.core.exceptions import ValidationError
@@ -67,7 +67,7 @@ class RelativeDateWrapper:
             if self.data.minutes_before is not None:
                 raise ValueError('A minute-based relative datetime can not be used as a date')
 
-            tz = ZoneInfo(event.settings.timezone)
+            tz = pytz.timezone(event.settings.timezone)
             if isinstance(event, SubEvent):
                 base_date = (
                     getattr(event, self.data.base_date_name)
@@ -86,7 +86,7 @@ class RelativeDateWrapper:
         if isinstance(self.data, (datetime.datetime, datetime.date)):
             return self.data
         else:
-            tz = ZoneInfo(event.settings.timezone)
+            tz = pytz.timezone(event.settings.timezone)
             if isinstance(event, SubEvent):
                 base_date = (
                     getattr(event, self.data.base_date_name)