protocol: remove unused create contract field

Author: xcolwell

protocol/transfer.pb.go

@@ -214,8 +214,10 @@ message CreateContract {
 
     // ulids
     repeated bytes intermediary_ids = 5;
-    // ulid
-    optional bytes stream_id = 6;
+    // optional bytes stream_id = 6 [deprecated=true];
+    reserved 6;
+    reserved "stream_id";
+
     // stream will be used when intermediary_ids or stream_id is set
     // in the case of wanting to use streams with no intermediaries, set `force_stream=true`
     optional bool force_stream = 7;