Revert the patch for MDEV-9504.
It causes test failures, attempt to fix these causes more failures. The
source of all this is that the code in test_if_skip_sort_order() has
a peculiar way of treating select_limit parameter:
Correct value is computed when the query plan is changed. In other cases,
we use an approximation that ignores the presence of GROUP BY clause,
or JOINs, or both.

A patch that fixes all of the above would be too big to do in 10.1