BUILD/MINOR: lua: ensure that hlua_ctx_destroy is properly defined

BUILD/MINOR: lua: ensure that hlua_ctx_destroy is properly defined

When Lua is disabled, the alternate functions must have the same
prototype as the original ones, otherwise we get such warnings :

src/stream.c:278:27: warning: too many arguments in call to 'hlua_ctx_destroy'
        hlua_ctx_destroy(&s->hlua);
        ~~~~~~~~~~~~~~~~         ^
No backport is needed.