remove bind-mounting certs test
remove bind-mounting certs test

we don't want this feature for 2.7; technically the code is there but
disabled by default. it was only in 2.7.x in the first place for reasons
that are no longer valid, so let's just wait for 2.8.

Signed-off-by: Clara Fu <d5c8bdbc15689555c92563892e959c79b3fc425f@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse