schema_tables: merge_tables_and_views: use drop_table_on_all_shards
schema_tables: merge_tables_and_views: use drop_table_on_all_shards

So that the dropped table's directory can be
removed after it has been dropped on all shards
if it has no snapshots.

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

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