sys/shell: remove ifdefs in the middle of code
sys/shell: remove ifdefs in the middle of code

ifdefs in the middle of code reduce the readability
and debugability and should be avoided.

Co-authored-by: Juan Carrano <b6181ad445abf6c9fa394b848854b3497b775b0d@fu-berlin.de>

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