Also, revert the work-around for the test that was attempted in
commit 85613a3247.
This issue was caught by MemorySanitizer as well as on the
Microsoft Windows debug builds, thanks to /MD being used
starting with 10.4.
The code fix will also be applied to 10.2 because the regression
was introduced in commit afc9d00c66.
For some reason, in the test main,innodb_ext_key,off
we frequently get unexpected EXPLAIN output, in particular
on Microsoft Windows debug builders. Let us comment out that
EXPLAIN statement for now.
