Safety check creates SQL aggregating error

[ScottVerbeek]

The SQL query here https://github.com/catalyst/moodle-local_datacleaner/blob/MOODLE_311_STABLE/cli/lib.php#L106-L112

Uses a group by statement incorrectly. Changing the select to select distinct and removing the group by will resolve the issue.

[ScottVerbeek]

The group by is actually completely redundant.

[picnicpete]

I had to fix a couple more little bugs to make the test run.
I did not create a unit test for this.

[ScottVerbeek]

The changes applied in #197 were only applied to branch MOODLE_311_STABLE. To close also port these changes to master and MOODLE_310_STABLE.

EDIT: And branch TOTARA_13.

[picnicpete]

There are pull requests for master and _310 branches. I have tested theses branches on my local docker-dev.
BTW: Those branches are looking very old. They have missed many updates that went to 311 branch. It might be time to close them off.

[ScottVerbeek]

The pull requests are merged. The branches may be older. The scope of this issue is will focus on that SQL what we have done. Feel free to create a new issue to maybe close down some branches.

There is still one branch remaining: TOTARA_13

[picnicpete]

Patches have been applied to master, MOODLE_310_STABLE, MOODLE_311_STABLE, and TOTARA_13 branches.