This effectively replaces xnmalloc, which perhaps should be deprecated.
The name xreallocarray should be easier to remember now that
reallocarray is a standard GNU function.
* lib/xalloc.h [GNULIB_XALLOC]: Do not include xalloc-oversized.h.
(xnmalloc, xnrealloc, x2nrealloc): Simplify by using xreallocarray.
* lib/xmalloc.c (xreallocarray): New function.
* modules/xalloc (Depends-on): Add reallocarray;
remove xalloc-oversized.