Mismatch between dir-spec.txt and routerparse.c

In #5041 (moved) we learned that leaving out contact lines from votes is permitted by the spec, but not by the code. I briefly compared dir-spec.txt and routerparse.c to find more mismatches between spec and code. Here's what I found:

• protocols lines are specified in dir-spec.txt and written to server descriptors, but they are not parsed in routerparse.c.

• consensus-method lines are specified as "Exactly once for consensuses" but implemented using the T01 macro in routerparse.c.

• contact lines are specified as "At most once" for votes and authority sections of consensuses, but are implemented using the T1 and T1N macro in routerparse.c.

• legacy-key-dir lines are specified as legacy-key in dir-spec.txt.

• s lines are specified as "At most once" in dir-spec.txt, but are implemented using the T1 macro in routerparse.c.

I didn't prepare a patch, because I didn't know whether to fix spec or code. If someone tells me, I can prepare one.