These were replaced by kmc in v17.0. We kept them as legacy alternatives
in v18.0, but it is time to remove them now to reduce the maintenance of
having multiple entry points to kmc.
Fixes: #13181
Test-bot: skip
1. Copy help.keyman.com/developer/17.0/* into /developer/docs/help
2. Update references to 18.0 where appropriate
3. Copy all referenced images from /cdn/dev into
/developer/docs/help/images and update links in documentation
Next commit: add deployment to help-keyman-com.sh. Note: simplest way to
test links at this point is to use the help.keyman.com auto deploy and
wait for the PR on help.keyman.com to be validated; we could look at an
internal link validation tool that verifies markdown links?
Relates-to: #12347
