remove removesuffix to support python 3.8

[th3w1zard1]

I needed a rtf parser for python 3.8 and this was the closest library I could find that met my purposes. Python 3.8 is the last supported python version on windows 7 which unfortunately I need to target.

This library contained a single incompatibility: removesuffix. Like most of 3.9's changes, it can easily be rewritten to support 3.8's functionality.

I have been using this library for over an hour and have not found any other incompatibilities with python 3.8.

if there are any other code segments this PR can backport please let me know.

[fleetingbytes]

Thanks for the PR, but I don't feel very compelled to merge it. Python 3.8 will be end-of-lifed in October 2024 (tomorrow). I understand that under Windows 7 you have no other option, but for that case you can use your fork. The other reason I don't want to merge it is that the current code base needs a clean up along the lines of Bob Martin's Clean Code guidelines. I may decide to make it compatible once I'll be refactoring it.