Remove link to `certificates/` page. (#202)
Remove link to `certificates/` page. (#202)

In f6e81a51112ca3ceff8baf9a114e45762eac3517 we removed the staging root
CA information from the `docs/certificates.md` page. This commit removes
the reference to the removed information from the
`staging-environment.md` page since it is no longer present.

Thanks to @tomwassenberg for reporting.
letsencrypt/website,letsencrypt/website,letsencrypt/website