remove flyspray (website/issue tracker down) (#3556)

- the repository at https://github.com/Flyspray/flyspray states: Please do not use Github for your bug reports or feature request. Instead use our live bug tracker at https://bugs.flyspray.org
- flyspray.org/bugs.flyspray.org: no such domain exists (https://dnschecker.org/)
- the bug tracker (itself a flyspray instance) is therefore also unreachable, leaving no way to contact maintainers
- hence not awesome
- ref. https://github.com/awesome-selfhosted/awesome-selfhosted/issues/2266

README.md

@@ -1955,7 +1955,6 @@ _Related: [Task Management & To-do Lists](#task-management--to-do-lists), [Softw
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 - [django-todo](http://django-todo.org/) - Pluggable, multi-user, multi-group, multi-list todo and ticketing system - a reusable app designed to be dropped into any existing Django project. ([Source Code](https://github.com/shacker/django-todo)) `BSD-3-Clause` `Python/Django`
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-- [Flyspray](https://www.flyspray.org/) - Uncomplicated, web-based bug tracking system. ([Source Code](https://github.com/Flyspray/flyspray)) `GPL-2.0` `PHP`
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