fix: removed skiff (defunct and shutting down in 6 months) (#1386)

You should remove Skiff since they are defunct and shutting down service in 6 months.  See <https://skiff.com/data-migration>.

README.md

@@ -194,7 +194,6 @@ Any comments, suggestions? [Let us know!](https://github.com/jaywcjlove/awesome-
 * [QOwnNotes](http://www.qownnotes.org/) - Open-source notepad with markdown support and todo list manager. [![Open-Source Software][OSS Icon]](https://github.com/pbek/QOwnNotes) ![Freeware][Freeware Icon]
 * [Quiver](http://happenapps.com/#quiver) - The Programmer's Notebook, lets you easily mix text, code, Markdown and LaTeX within one note, edit code with an awesome code editor and live preview Markdown and LaTeX.
 * [AliYuQue](https://www.yuque.com/install/desktop) - Cloud note-taking knowledge management, collaboration platform, Markdown based writing, support embedded flow chart, brain diagram, timing sequence, code rendering, Sketch board creation, personal knowledge sharing, etc. Compared to youdao cloud note and evernote similar products, which include all of its functions, support knowledge sharing and more powerful creation, collaboration and editor, it comes from alibaba ant financial.![Freeware][Freeware Icon]
-* [Skiff](https://skiff.com/) - End-to-end encrypted & decentralized email, real-time document collaboration, and file storage designed with zero-trust privacy -- available on web, iOS/Android, and macOS. ![Freeware][Freeware Icon][![Open-Source Software][OSS Icon]](https://github.com/skiff-org)
 * [VNote](https://app.vnote.fun/) - A Qt-based application designed to provide a pleasant note-taking platform with excellent editing experience. [![Open-Source Software][OSS Icon]](https://github.com/vnotex/vnote/) ![Freeware][Freeware Icon]
 
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