graph+routing: address linter errors

This is done in a separate commit so as to keep the original code-move
commit mostly a pure code move.

graph/log.go

@@ -18,7 +18,7 @@ func init() {
 }
 
 // DisableLog disables all library log output.  Logging output is disabled by
-// by default until UseLogger is called.
+// default until UseLogger is called.
 func DisableLog() {
 	UseLogger(btclog.Disabled)
 }