Re-design of a way for handling the DELETE statement introduced by
the task MDEV-28883, added regression caused by missing reset of
the data member current_select->first_cond_optimization on handling
the DELETE statement that results in a memory leaks on second execution
of the same DELETE statement in PS mode.

To fix memory leaks, added set of the data member
  current_select->first_cond_optimization
to the value false on finishing execution of DELETE statement.