seL4_libs: remove autoconf.h from seL4_libs

this commit removes autoconf.h generation from each lib and
append '#include <<lib_name>/gen_config.h>' after each
'#include <autoconf.h>' since autoconf.h is only the for the
kernel config now. This is a temporarily solution, since we
currently don't have a way to tell which header files each file
is trying to include when it includes 'autoconf.h'

pragma once and for all

Fix licenses

Remove #ifdef guards for the existance of different libraries

These libraries are now all part of this same repository, and so they will always exist.
Guarding for them adds unnecessary complexity