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/erasure-healing_test.go

@@ -163,7 +163,7 @@ func TestHealingDanglingObject(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	//defer removeRoots(fsDirs)
+	defer removeRoots(fsDirs)
 
 	// Everything is fine, should return nil
 	objLayer, disks, err := initObjectLayer(ctx, mustGetPoolEndpoints(fsDirs...))