bt_*, hex, base32z, base64 all moved to oxen-encoding a while ago; this
finishes the move by removing them from oxenmq and instead making oxenmq
depend on oxen-encoding.
The existing code was overly complicated by trying to track indices in
the `connections` vector, which complication happening because things
get removed from `connections` requiring all the internal index values
to be updated. So we ended up with a connection ID inside the
ConnectionID object, plus a map of those connection IDs to the
`connections` index, and need a map back from indices to ConnectionIDs.
Though this seems to work usually, I recently noticed an
oxen-storage-server sending oxend requests on the wrong connection and
so I suspect there is some rare edge cases here where a failed
connection index might not be updated properly.
This PR simplifies the whole thing by making getting rid of connection
ids entirely and keeping the connections in a map (with connection ids
that never change). This might end up being a little less efficient
than the vector, but it's unlikely to matter and the added complexity
isn't worth it.
Sean Darcy
Jason Rhinelander