zuul: drop dupe file reference in production

role::zuul::production defined a file { '/srv/ssd/git' } which is also
passed as $git_dir to the module which then creates a file { $git_dir }
ending up with a dupe reference.

this patch removes the file{} statement in the role class. We should
later on ensure we have /srv/ssd mounted though. I have left a note
about it.

Change-Id: Id6fc1c59fe01044617fd27ee7a82fb048e76b9da
Merge "zuul: drop dupe file reference in production" into production