schema_tables: Add scylla_tables to ALL
schema_tables: Add scylla_tables to ALL

So that scylla_tables takes part in the digest and in mutations sent
as part of schema sync. Otherwise inconsistencies in scylla_tables
will not heal.

Refs #2608.

avikivity/scylla,duarten/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla