protect remaining uses of prov_hash against concurrent access

protect remaining uses of prov_hash against concurrent access

* setup.c (hash_get_prov_list): New function.
* setup.h: Declare it.
* replica.c (replicate, replicate_namespace_action): Use
hash_get_prov_list to get all provider pointers at once, and which
locks the hash table before accessing it.
With hash_get_first_prov and hash_get_next_prov that was not possible.
* setup.c (hash_get_first_prov, hash_get_next_prov): Remove functions.
* setup.h: Remove declarations.