Remove "logger" field from config.json (#5268)

File logging removed as part of improvement to server logging.

config.json format updated to version 21.

Fixes #5176

cmd/server-main.go

@@ -147,9 +147,6 @@ func serverMain(ctx *cli.Context) {
 	// Initialize server config.
 	initConfig()
 
-	// Enable loggers as per configuration file.
-	enableLoggers()
-
 	// Init the error tracing module.
 	errors.Init(GOPATH, "github.com/minio/minio")