token_metadata: use mutable_token_metadata_ptr in calculate_pending_ranges_for_*
token_metadata: use mutable_token_metadata_ptr in calculate_pending_ranges_for_*

Replacing old code using lw_shared_ptr<token_metadata> with the "modern"
mutable_token_metadata_ptr alias.

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla