Revert "Make message for UnknownPeersError more meaningful"

This reverts commit 752cfdcb6770945ca554d20392d1545cf7a59edd.
Revert "Change iteration over connection decoding to abort after the first error, and let the UnknownPeersError know which peer was unknown"

This reverts commit 978d374820098ed509de4f08ff96afc49da79093.
Remove message about unknown peer from the log