tests/unittests: remove the 'DISABLE_TEST_FOR_ARCH'
tests/unittests: remove the 'DISABLE_TEST_FOR_ARCH'

Remove the arch disabling tests handling as now unused.

If something like this is necessary again the test must be put
outside of unittests.

aeneby/RIOT,ant9000/RIOT,OTAkeys/RIOT,miri64/RIOT,mtausig/RIOT,aeneby/RIOT,toonst/RIOT,OTAkeys/RIOT,smlng/RIOT,OlegHahm/RIOT,kaspar030/RIOT,ant9000/RIOT,OlegHahm/RIOT,cladmi/RIOT,jasonatran/RIOT,OTAkeys/RIOT,yogo1212/RIOT,ant9000/RIOT,basilfx/RIOT,ant9000/RIOT,mtausig/RIOT,josephnoir/RIOT,basilfx/RIOT,toonst/RIOT,x3ro/RIOT,mtausig/RIOT,toonst/RIOT,miri64/RIOT,smlng/RIOT,cladmi/RIOT,OTAkeys/RIOT,yogo1212/RIOT,toonst/RIOT,miri64/RIOT,kaspar030/RIOT,cladmi/RIOT,ant9000/RIOT,authmillenon/RIOT,rfuentess/RIOT,yogo1212/RIOT,authmillenon/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,authmillenon/RIOT,smlng/RIOT,kYc0o/RIOT,kaspar030/RIOT,cladmi/RIOT,RIOT-OS/RIOT,cladmi/RIOT,mtausig/RIOT,kYc0o/RIOT,yogo1212/RIOT,jasonatran/RIOT,rfuentess/RIOT,x3ro/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,miri64/RIOT,aeneby/RIOT,kYc0o/RIOT,x3ro/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,josephnoir/RIOT,miri64/RIOT,kYc0o/RIOT,x3ro/RIOT,jasonatran/RIOT,x3ro/RIOT,basilfx/RIOT,authmillenon/RIOT,josephnoir/RIOT,rfuentess/RIOT,aeneby/RIOT,smlng/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,josephnoir/RIOT,jasonatran/RIOT,kaspar030/RIOT,authmillenon/RIOT,toonst/RIOT,aeneby/RIOT,mtausig/RIOT,kaspar030/RIOT,rfuentess/RIOT,yogo1212/RIOT,josephnoir/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,basilfx/RIOT,yogo1212/RIOT,kYc0o/RIOT,rfuentess/RIOT,smlng/RIOT,basilfx/RIOT