Fix dir-spec: there is not actually any such item as link-key. (Found by Benedikt.)
svn:r10095
Every router descriptor MUST start with a "router" Item; MUST end with a
"router-signature" Item and an extra NL; and MUST contain exactly one
instance of each of the following Items: "published" "onion-key"
- "link-key" "signing-key" "bandwidth".
+ "signing-key" "bandwidth".
A router descriptor MAY have zero or one of each of the following Items,
but MUST NOT have more than one: "contact", "uptime", "fingerprint",