Downgrades a valid log (#2057)

## Issue Addressed

#2046 

## Proposed Changes

The log was originally intended to verify the correct logic and ordering of events when scoring peers. The queued tasks can be structured in such a way that peers can be banned after they are disconnected. Therefore the error log is now downgraded to  debug log.

beacon_node/network/Cargo.toml

@@ -13,6 +13,7 @@ tempfile = "3.1.0"
 exit-future = "0.2.0"
 slog-term = "2.6.0"
 slog-async = "2.5.0"
+logging = { path = "../../common/logging" }
 
 [dependencies]
 beacon_chain =  { path = "../beacon_chain" }