malloc: Remove malloc hooks from fork handler

The fork handler now runs so late that there is no risk anymore that
other fork handlers in the same thread use malloc, so it is no
longer necessary to install malloc hooks which made a subset
of malloc functionality available to the thread that called fork.

malloc/malloc.c

@@ -1074,8 +1074,6 @@ static void*   realloc_check(void* oldmem, size_t bytes,
 			       const void *caller);
 static void*   memalign_check(size_t alignment, size_t bytes,
 				const void *caller);
-static void*   malloc_atfork(size_t sz, const void *caller);
-static void      free_atfork(void* mem, const void *caller);
 
 /* ------------------ MMAP support ------------------  */