multi: add NewLogClosure in lnutils to avoid repetition

And replaces all usage of `logClosure` with `lnutils.LogClosure`.

graph/builder.go

@@ -1432,7 +1432,9 @@ func (b *Builder) processUpdate(msg interface{},
 		}
 
 		log.Tracef("New channel update applied: %v",
-			newLogClosure(func() string { return spew.Sdump(msg) }))
+			lnutils.NewLogClosure(func() string {
+				return spew.Sdump(msg)
+			}))
 		b.stats.incNumChannelUpdates()
 
 	default:

graph/log.go

@@ -29,19 +29,3 @@ func DisableLog() {
 func UseLogger(logger btclog.Logger) {
 	log = logger
 }
-
-// logClosure is used to provide a closure over expensive logging operations so
-// don't have to be performed when the logging level doesn't warrant it.
-type logClosure func() string
-
-// String invokes the underlying function and returns the result.
-func (c logClosure) String() string {
-	return c()
-}
-
-// newLogClosure returns a new closure over a function that returns a string
-// which itself provides a Stringer interface so that it can be used with the
-// logging system.
-func newLogClosure(c func() string) logClosure {
-	return logClosure(c)
-}