DOCS: Update documentation to remove `--wait` flag

[dylan-smith]

In the docs where showing how to migrate a single repo the example command has --wait which is no obsolete. The docs should be updated to remove all mentions of --wait. And if there is anywhere where we talk about doing parallel migrations (I don't think we do in the docs), they should be updated to use --queue-only flag.

Here's at least one spot in the docs that needs to be updated:
https://docs.github.com/en/migrations/using-github-enterprise-importer/migrating-repositories-with-github-enterprise-importer/migrating-repositories-from-githubcom-to-github-enterprise-cloud#migrate-a-single-repository