Remove mallocarray(...) and use reallocarray(NULL, ...)

After a short correspondence with Otto Moerbeek it turned out
mallocarray() is only in the OpenBSD-Kernel, because the kernel-
malloc doesn't have realloc.
Userspace applications should rather use reallocarray with an
explicit NULL-pointer.

Assuming reallocarray() will become available in c-stdlibs in the
next few years, we nip mallocarray() in the bud to allow an easy
transition to a system-provided version when the day comes.

util.h

@@ -25,8 +25,6 @@ void apathmax(char **, size_t *);
 
 void *ecalloc(size_t, size_t);
 void *emalloc(size_t);
-void *mallocarray(size_t, size_t);
-void *emallocarray(size_t, size_t);
 void *erealloc(void *, size_t);
 void *reallocarray(void *, size_t, size_t);
 void *ereallocarray(void *, size_t, size_t);