Remove deprecated features

As per #10730, v2.16 deprecated these features and scheduled them for removal in v2.18:

- `IdoMySqlConnection` and `IdoPgsqlConnection`
- `CompatLogger`
- `ExternalCommandListener`
- `LivestatusListener`
- `ElasticsearchWriter`
- Namespace definitions in DSL
- Bundled `check_*.exe` plugins on Windows