Commit b5615eff introduced comment in result file during shutdown.
In case of Windows for the tests involving `file_key_managment.so` as plugin-load-add the tests will be overwritten with .dll extension.
The same happens with environment variable `$FILE_KEY_MANAGMENT_SO`.
So the patch is removing the extension to be extension agnostic.

Reviewed by: wlad@mariadb.com