Remove obsolete marker line

doc/set-up-gdk.md

@@ -93,8 +93,3 @@ You can override the port used by this GDK with a 'port' file.
 If you want to work on GitLab CI you will need to install [GitLab Runner](https://gitlab.com/gitlab-org/gitlab-ci-multi-runner).
 To enable the OpenLDAP server, see the OpenLDAP instructions in this readme.
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-END Post-installation
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-Please do not delete the 'END Post-installation' line above. It is used to
-print the post-installation message from the `Makefile`.