Remove deprecated Object(json) type

[mshustov]

The legacy experimental JSON type implementation (Object('json')) has been deprecated https://clickhouse.com/docs/sql-reference/data-types/object-data-type in favour of new implementation https://clickhouse.com/blog/a-new-powerful-json-data-type-for-clickhouse

The legacy JSON type is about to be removed from the ClickHouse codebase ClickHouse/ClickHouse#85718.
Since the legacy implementation is marked as experimental, we can consider removing it from the codebase without backward compatibility with LTS ClickHouse versions.