Cherry-pick #9802 to 6.x: Remove X-Pack foo Metricbeat module

[sayden]

Cherry-pick of PR #9802 to 6.x branch. Original message:

The purpose of the foo module in Metricbeat X-Pack was to test the new build and test system within the x-pack/metricbeat folder.

After merging MS SQL module in X-Pack, we can already remove this dummy module.

Things that have been removed:

• module folder and all its contents module/foo
• References to the module and metricset in include/list.go file
• Reference in the metricbeat.reference.yml file.

[ruflin]

How did this end up in 6.x? Do we have this also in 6.6?

[sayden]

I was also surprised and yes, we also have it in 6.6 so I'm gonna open a new PR to remove it from there.

[ruflin]

Yes, please also remove it from there. As we don't have any x-pack modules in 6.6 AFAIK, I wonder how this ended up here. Could you investigate as I worry that also other things potentially ended up here?

[sayden]

metricbeat.reference.yml with module: foo was added to master here #9242 on Nov 27 (exactly one month ago)

Few days later, ILM support was added to Master here #7963 and cherry picked to 6.x here #9418 and I guess it got into 6.6 when we did the release few days ago.

[ruflin]

I see, seems like we missed that during the review and for some reason the reference file is not generated correctly in 6.x as otherwise make check should have detected this. Let's also remove it from 6.6.