Remove error TODO

Remove the TODO from comments and raise a GitHub issue to track it.

  https://github.com/rust-bitcoin/rust-bitcoin/issues/1002

src/blockdata/script.rs

@@ -196,7 +196,7 @@ impl std::error::Error for Error {
             NonMinimalPush
             | EarlyEndOfScript
             | NumericOverflow
-            | BitcoinConsensus(_) // TODO: This should return `Some` but bitcoinconsensus::Error does not implement Error.
+            | BitcoinConsensus(_)
             | UnknownSpentOutput(_)
             | SerializationError => None,
         }