Fix the known issue with the DSA

I wrote it to only select TXs with a timelock, not only TXs which are unlocked.
This most likely explains why it so heavily selected coinbases.

Also moves an InternalError which would've never been hit on mainnet, yet
technically isn't an invariant, to only exist when cfg(test).

coins/monero/src/wallet/scan.rs

@@ -273,7 +273,11 @@ impl<O: Clone + Zeroize> Timelocked<O> {
   /// Returns None if the Timelocks aren't comparable. Returns Some(vec![]) if none are unlocked.
   pub fn unlocked(&self, timelock: Timelock) -> Option<Vec<O>> {
     // If the Timelocks are comparable, return the outputs if they're now unlocked
-    self.0.partial_cmp(&timelock).filter(|_| self.0 <= timelock).map(|_| self.1.clone())
+    if self.0 <= timelock {
+      Some(self.1.clone())
+    } else {
+      None
+    }
   }
 
   pub fn ignore_timelock(&self) -> Vec<O> {