CONTRIBUTING: remove 'feature request' and 'bug reports' sections
CONTRIBUTING: remove 'feature request' and 'bug reports' sections

These have fairly clear templates in the GitHub interface.
Duplicating that here servers no purpose.

jasonatran/RIOT,ant9000/RIOT,kaspar030/RIOT,miri64/RIOT,miri64/RIOT,ant9000/RIOT,kaspar030/RIOT,miri64/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,kaspar030/RIOT,miri64/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,authmillenon/RIOT,jasonatran/RIOT,ant9000/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,kaspar030/RIOT,OTAkeys/RIOT,jasonatran/RIOT,authmillenon/RIOT,jasonatran/RIOT,authmillenon/RIOT,kYc0o/RIOT,kYc0o/RIOT,OlegHahm/RIOT,authmillenon/RIOT,jasonatran/RIOT,authmillenon/RIOT,ant9000/RIOT,kYc0o/RIOT,kYc0o/RIOT,OTAkeys/RIOT,kaspar030/RIOT,ant9000/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,miri64/RIOT