Remove disabled challenges from the list of targets
Remove disabled challenges from the list of targets

Challenges 31 and 32 can not be launched from the root level Makefile,
since their execution is a bit more complicated than the rest of the
exercices. However their presence (even disabled) in the list of
potentials targets made the command "make all" crash.

lucasg/Cryptopals,lucasg/Cryptopals,lucasg/Cryptopals,lucasg/Cryptopals