Resolve #360 (#456)

* Remove NetworkId from processor-messages

Because intent binds to the sender/receiver, it's not needed for intent.

The processor knows what the network is.

The coordinator knows which to use because it's sending this message to the
processor for that network.

Also removes the unused zeroize.

* ProcessorMessage::Completed use Session instead of key

* Move SubstrateSignId to Session

* Finish replacing key with session

common/db/src/create_db.rs

@@ -51,12 +51,10 @@ macro_rules! create_db {
             ($($arg),*).encode()
           )
         }
-        #[allow(dead_code)]
         pub fn set(txn: &mut impl DbTxn $(, $arg: $arg_type)*, data: &$field_type) {
           let key = $field_name::key($($arg),*);
           txn.put(&key, borsh::to_vec(data).unwrap());
         }
-        #[allow(dead_code)]
         pub fn get(getter: &impl Get, $($arg: $arg_type),*) -> Option<$field_type> {
           getter.get($field_name::key($($arg),*)).map(|data| {
             borsh::from_slice(data.as_ref()).unwrap()