Disable crond if LetsEncrypt disabled

Previously the Omnibus-provided crond would still run if LetsEncrypt were enabled and then disabled later. This also goes for the auto-renew configuration. In both cases, crond is not needed, so we can disable the service if LetsEncrypt is not used. This also prevents stale configuration files from lingering.

While this isn't technically a regression, the upgrade of go-crond exposed this problem because the configuration flags changed, and Omnibus was no longer managing the runit files.

Closes #5541 (closed)