log, internal/debug: delete RotatingFileHandler (#20586)

* log: delete RotatingFileHandler

We added this for the dashboard, which is gone now. The
handler never really worked well and had data race and file
handling issues.

* internal/debug: remove unused RotatingFileHandler setup code

cmd/devp2p/main.go

@@ -45,7 +45,7 @@ func init() {
 	// Set up the CLI app.
 	app.Flags = append(app.Flags, debug.Flags...)
 	app.Before = func(ctx *cli.Context) error {
-		return debug.Setup(ctx, "")
+		return debug.Setup(ctx)
 	}
 	app.After = func(ctx *cli.Context) error {
 		debug.Exit()