The ctrl-home and ctrl-end keybindings are provided by the Scintilla editing widget that Geany uses and are documented [here](http://www.geany.org/manual/current/index.html#keyboard-commands)
Since they are not provided by Geany they can't be undefined, but since Geany keybindings override Scintilla ones, you can define them to something in Geany that annoys you less, maybe an undefined custom command.