Clean up MAINTAINERS files

* Remove out of date "vacation mode"
* Fix my email address
* Remove infrastructure maintainers to reflect reality (core maintainers
are currently maintaining their own infrastructure).

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Merge pull request #5331 from shykes/cleanup-maintainers

Clean up MAINTAINERS files