Refactor: libpe_status, libpacemaker: Drop pe_hash_table_lookup()

It's used only with pe_resource_t:allowed_nodes and
pe_resource_t:known_on hash tables. Both of those are guaranteed
non-NULL at resource unpack time and are only set back to NULL at
resource free time.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>