[Findit] Fix flaky tests due to importing pytz.

appengine/findit/common/time_util.py

Index: appengine/findit/common/time_util.py
diff --git a/appengine/findit/common/time_util.py b/appengine/findit/common/time_util.py
index 407ed700f72e2dc11212c30d2be6190a907157bb..daebcc115d2f9ca6bccd6607982afc20bf6739a6 100644
--- a/appengine/findit/common/time_util.py
+++ b/appengine/findit/common/time_util.py
@@ -45,16 +45,15 @@ def FormatDatetime(date):
     return date.strftime('%Y-%m-%d %H:%M:%S UTC')
 
 
-def GetDatetimeInTimezone(timezone_name, date_time=None):
+def GetDatetimeInTimezone(timezone_name, date_time):
   """Returns the datetime.datetime of the given one in the specified timezone.
 
   Args:
     timezone_name (str): The name of any timezone supported by pytz.
     date_time (datetime.datetime): The optional datetime to be converted into
-        the new timezone. If not given, default to UTC now.
+        the new timezone.
 
   Returns:
     A datetime.datetime of the given one in the specified timezone.
   """
-  date_time = date_time or GetUTCNowWithTimezone()
   return date_time.astimezone(pytz.timezone(timezone_name))