Remove old credits and refer to the new SEF credits

[T-MaxWiese-T]

I looked at the SwatCredits file and it would be too much work to rework everything so I decided to remove the old credits completely especially because nobody looks at the length of the credits. Therefore you should refer to GitHub where the relevant credits for SEF are. A positive side effect would be that the credits would be more present and more people would be encouraged to contribute to SEF or maybe donate. Furthermore, the work of the modders would be more appreciated.