'status' subcommand should not include ".git-crypt/" directory

for example, `git-crypt status` says something like this:

```
...
encrypted: my.secret
not encrypted: .git-crypt/.gitattributes
not encrypted: .git-crypt/keys/default/0/DEADBEAF.gpg
```

but we already know that... really, the git-crypt metadata dir
should not be displayed by `status` (it's essentially metadata,
and should be considered as "out of band" information).