malloc: Update heap dumping/undumping comments [BZ #23351]

Also remove a few now-unused declarations and definitions.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

malloc/malloc.c

@@ -697,22 +697,6 @@ size_t   __malloc_usable_size(void*);
 */
 void     __malloc_stats(void);
 
-/*
-  malloc_get_state(void);
-
-  Returns the state of all malloc variables in an opaque data
-  structure.
-*/
-void*  __malloc_get_state(void);
-
-/*
-  malloc_set_state(void* state);
-
-  Restore the state of all malloc variables from data obtained with
-  malloc_get_state().
-*/
-int      __malloc_set_state(void*);
-
 /*
   posix_memalign(void **memptr, size_t alignment, size_t size);