Hi Andreas,
This is a launchpad configuration parameter. Are you familiar with setting launchpad configuration parameters? You can set this directly in the Fiori Launchpad HTML file or you can set it in a configuration file that can then be linked into the HTML file or appended as an URL parameter.
You need to set enableHideGroups=true
Please note that this parameter cannot be set directly as a URL parameter.
You can refer to this help documentation, which really outlines the options quite well:
http://help.sap.com/saphelp_scm700_ehp03/helpdata/en/61/07ee41f89a43c9af0aa279fe039cca/content.htm
Good luck and best regards