Remove com.ddev.container-type from documentation

[tmotyl]

PR #215 has changed the com.ddev.container-type label to
com.docker.compose.service.

Documentation https://ddev.readthedocs.io/en/latest/users/extend/custom-compose-files/
and solr example needs to be updated.

[tannerjfco]

This is actually a label that was deprecated some time ago, and should be removed from the documentation. ddev uses the com.docker.compose.service label provided by docker-compose to determine the 'container type'.

[tmotyl]

updated the issue description and PR to match comment from @tannerjfco

[tannerjfco]

Thanks for the update! We actually don't need to define com.docker.compose.service anywhere though, as it's provided automatically by docker-compose to match the name of the service. If we just remove the label from the documented list of labels a custom service should provide, I think we'll be all set here. Sorry for the confusion, and thanks for the attention to this!

[tmotyl]

here you go

[tannerjfco]

Thanks again for the attention paid to this and the clean up