Readme: remove links to different preview variants

The links to the different preview variants are no longer
needed in the readme, as they are provided in different
places:

1. The GFM variant is set as 'default' in the repo
2. There is a link to the Docsify version in the repo
3. Direct links to both variants are provided in ILIAS

This section has been removed to improve readability.

Author: cagix

readme.md

@@ -51,17 +51,6 @@ Studierendenservice bekanntgegeben. (vgl. LSF und [Ankündigungen])
 
 * * * * *
 
----
-
-::: tip
-**Read Online**:
-
-*   [GitHub Preview](https://github.com/Programmiermethoden-CampusMinden/PM-Lecture/blob/_gfm/readme.md)
-*   [Docsify Preview](https://docsify-this.net/?basePath=https://raw.githubusercontent.com/Programmiermethoden-CampusMinden/PM-Lecture/refs/heads/_docsify&homepage=readme.md&sidebar=true&browser-tab-title=PM&font-size=14px&searchbox=true&externalLinkTarget=_blank&mergeNavbar=true&zoom-images=true&dark-mode=auto#/)
-:::
-
----
-
 
 # Kursbeschreibung