Remove hidden dependency to 3rd party module python-dateutil

[rcrdnalor]

• Platform: Linux

• MythTV version: master and v31

• Package version:

• Component: MythTV Python Bindings

What steps will reproduce the bug?

Run the grabber 'tvmaze.py' without installed package 'python-dateutil' results to trace back
'ModuleNotFound'

How often does it reproduce? Is there a required condition?

Every time

What is the expected behaviour?

No traceback, functional graber instead

What do you see instead?

Traceback complaining about 'ModuleNotFound'

Additional information

The new grabber tvmaze.py introduced a hidden dependency to
the parser inside the package python-dateutil:
from dateutil import parser

Note: The python module 'dateutil' provides time zone support
for the python 'datetime' module and is outdated in favor
of the new zone info module
https://docs.python.org/3/library/zoneinfo.html
MythTV's python package already provides IANA time zone support
within it's custom implementation of 'datetime'.

Given the fact, that most of the distributions do not install
python-dateutil or python3-dateutil by default anymore,
we need to either remove it, or declare it as an official
dependency.

[rcrdnalor]

Implemented on master by 99c3ec2