remove hack for debian etch limits.h

remove hack for debian etch limits.h

The debian etch distro was end-of-life a long time ago so we no
longer need the ULLONG_MAX hack. In any case gnulib now provides
an equivalent fix by default, and so our definition now triggers
syntax-check rule failure

src/internal.h:#    define ULLONG_MAX   ULONG_LONG_MAX
maint.mk: define the above via some gnulib .h file
maint.mk:843: recipe for target 'sc_prohibit_always-defined_macros' failed

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>