It is never called after 7fb9d649, which makes the whole refresh version
infrastructure useless.

Removed:
- tdc_version_t
- TDC_VERSION_MAX
- tdc_version
- TDC_element::version
- tdc_increment_refresh_version()
- tdc_refresh_version()
- refresh_version argument of tdc_wait_for_old_version()
- Flush_commands status variable
- refresh version from COM_STATISTICS
- refresh version from dbug printouts

Part of MDEV-17882 - Cleanup refresh version