Removed tdc_increment_refresh_version()

It is never called after 7fb9d64, 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

sql/sql_test.cc

@@ -110,8 +110,6 @@ static void print_cached_tables(void)
 
   tdc_iterate(0, (my_hash_walk_action) print_cached_tables_callback, NULL, true);
 
-  printf("\nCurrent refresh version: %ld\n",
-         (long) tdc_refresh_version());
   fflush(stdout);
   /* purecov: end */
   return;