Remove VectorClock type (#235)

We are no longer referring to this as a 'vector clock', instead it could be more accurately called a cursor.

proto/mls_validation/v1/service.proto

@@ -4,7 +4,6 @@ package xmtp.mls_validation.v1;
 
 import "identity/api/v1/identity.proto";
 import "identity/associations/association.proto";
-import "identity/associations/signature.proto";
 import "identity/credential.proto";
 
 option go_package = "github.com/xmtp/proto/v3/go/mls_validation/v1";

proto/xmtpv4/envelopes/envelopes.proto

@@ -10,16 +10,15 @@ import "mls/api/v1/mls.proto";
 option go_package = "github.com/xmtp/proto/v3/go/xmtpv4/envelopes";
 
 // The last seen entry per originator. Originators that have not been seen are omitted.
-// Entries MUST be sorted in ascending order, so that smaller node ID's appear first.
-message VectorClock {
+message Cursor {
   map<uint32, uint64> node_id_to_sequence_id = 1;
 }
 
 // Data visible to the server that has been authenticated by the client.
 message AuthenticatedData {
   uint32 target_originator = 1;
   bytes target_topic = 2;
-  VectorClock last_seen = 3;
+  Cursor last_seen = 3;
 }
 
 message ClientEnvelope {

proto/xmtpv4/message_api/message_api.proto

@@ -15,7 +15,7 @@ message EnvelopesQuery {
   repeated bytes topics = 1;
   // Node queries
   repeated uint32 originator_node_ids = 2;
-  xmtp.xmtpv4.envelopes.VectorClock last_seen = 3;
+  xmtp.xmtpv4.envelopes.Cursor last_seen = 3;
 }
 
 // Batch subscribe to envelopes