ATS11: Remove slow log feature

## Summary

Remove the built-in slow log feature from ATS. This functionality is better handled by log analysis tools and custom logging configurations rather than baked into the core.

## Files to modify

The slow log touches the following areas:

### Core
- `src/proxy/http/HttpSM.cc` - slow log logic in HTTP state machine
- `src/proxy/http/HttpConfig.cc` - slow log config handling
- `include/proxy/http/HttpConfig.h` - slow log config structs
- `include/proxy/http/OverridableConfigDefs.h` - overridable config entries

### H2
- `src/proxy/http2/Http2Stream.cc` - H2 slow log integration
- `src/proxy/http2/Http2CommonSession.cc` - H2 session slow log
- `src/proxy/http2/HTTP2.cc` - H2 slow log config
- `include/proxy/http2/HTTP2.h` - H2 slow log declarations

### Records / Config
- `src/records/RecordsConfig.cc` - slow log record definitions
- `configs/records.yaml.default.in` - default config values

### Logging
- `configs/logging.yaml.default` - slow log format definition

### Cripts
- `include/cripts/Configs.hpp` - cripts slow log bindings

### Documentation
- `doc/admin-guide/files/records.yaml.en.rst`
- `doc/developer-guide/api/functions/TSHttpOverridableConfig.en.rst`
- `doc/locale/ja/LC_MESSAGES/developer-guide/api/functions/TSHttpOverridableConfig.en.po`

### Tests
- `tests/gold_tests/records/legacy_config/full_records.config`