Scenario:
When Populate holiday time on the timesheet option is enabled, it would populate the holiday hours automatically on the user’s timesheet.
It will also create a Time Off Booking which can be seen in the Historical TimeOff page. When you delete this Time Off Booking from the Historical Time Off page, Web TimeSheet will not send Time Off booking is
deleted email notification to the user.

The Time Off booking is deleted email notification will be sent to the user, only when a Time Off Booking submitted by an user is deleted.
Since a autopopulated Holiday Time Off was submitted by the system and not by a user, a notification e-mail is not sent to the user when the Time Off booking is deleted.