safe-alloc: make obsolete and remove REALLOC_N Problem reported by Vivien Kraus in: https://lists.gnu.org/r/bug-gnulib/2025-07/msg00073.html This module never caught on. * lib/safe-alloc.h (REALLOC_N): Remove. * modules/safe-alloc: Now obsolete. * tests/test-safe-alloc.c (main): Remove REALLOC_N test.