Add void return type to all *_alter hook implementations

This has exposed a few alter hooks that are erroneously returning something.

Looks good!

Great catch on the ones that returned values.

Needs a rebase.

Rebased

@mstrelan, thanks for the quick turn around. I was just finishing my review earlier when we had a power outage so this had to wait a bit.

Committed to 11.x and 11.1.x.

Thanks!

quietone → closed merge request !10198

Automatically closed - issue fixed for 2 weeks with no activity.