WL#9680: Remove unused date_format, datetime_format, time_format, max_tmp_tables

Affects: Server-8.0   —   Status: Complete   —   Priority: Medium

Remove items never used,  deprecated in 5.6:

* date_format, datetime_format, time_format, max_tmp_tables system variables
F1)Remove system variables: date_format, datetime_format, time_format,
max_tmp_tables.