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/bucket-policy.go

@@ -172,11 +172,12 @@ func getConditionValues(r *http.Request, lc string, username string, claims map[
 		vStr, ok := v.(string)
 		if ok {
 			// Special case for AD/LDAP STS users
-			if k == ldapUser {
+			switch k {
+			case ldapUser:
 				args["user"] = []string{vStr}
-			} else if k == ldapUserN {
+			case ldapUserN:
 				args["username"] = []string{vStr}
-			} else {
+			default:
 				args[k] = []string{vStr}
 			}
 		}