Remove activity table and model (#40017)

...ckend/src/metabase_enterprise/serialization/v2/models.clj

...ackend/test/metabase_enterprise/models/entity_id_test.clj

resources/migrations/001_update_migrations.yaml

src/metabase/cmd/copy.clj

src/metabase/models.clj

src/metabase/models/activity.clj

src/metabase/models/audit_log.clj

test/metabase/api/session_test.clj

test/metabase/db/schema_migrations_test.clj

test/metabase/test/generate.clj