We already use the new pending_endpoints from erm though
the get_pending_ranges virtual function, in this commit
we update all the remaining places to use the new
implementation in erm, as well as remove the old implementation
in token_metadata.
We want to switch token_metadata_test to the new
implementation of pending_endpoints and read_endpoints in erm.
To do this, it is convenient to have token_metadata and
replication_strategy as shared pointers, as it fits better with the signature
of calculate_effective_replication_map. In this commit we don't
change the logic of the tests, we just migrate them to use pointers.
