add gocritic/ruleguard checks back again, cleanup code. (#13665)

- remove some duplicated code
- reported a bug, separately fixed in #13664
- using strings.ReplaceAll() when needed
- using filepath.ToSlash() use when needed
- remove all non-Go style comments from the codebase

Co-authored-by: Aditya Manthramurthy <donatello@users.noreply.github.com>

cmd/config-versions.go

@@ -34,14 +34,12 @@ import (
 	"github.com/minio/pkg/quick"
 )
 
-/////////////////// Config V1 ///////////////////
 type configV1 struct {
 	Version   string `json:"version"`
 	AccessKey string `json:"accessKeyId"`
 	SecretKey string `json:"secretAccessKey"`
 }
 
-/////////////////// Config V2 ///////////////////
 type configV2 struct {
 	Version     string `json:"version"`
 	Credentials struct {
@@ -63,7 +61,6 @@ type configV2 struct {
 	} `json:"fileLogger"`
 }
 
-/////////////////// Config V3 ///////////////////
 // backendV3 type.
 type backendV3 struct {
 	Type  string   `json:"type"`