cherry-pick: home: rm unnecessary locking in update; refactor

Merge in DNS/adguard-home from 4499-rm-unnecessary-locking to master

Squashed commit of the following:

commit 6d70472506dd0fd69225454c73d9f7f6a208b76b
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Apr 25 17:26:54 2022 +0300

    home: rm unnecessary locking in update; refactor

internal/aghnet/net_openbsd.go

@@ -13,10 +13,6 @@ import (
 	"github.com/AdguardTeam/AdGuardHome/internal/aghos"
 )
 
-func canBindPrivilegedPorts() (can bool, err error) {
-	return aghos.HaveAdminRights()
-}
-
 func ifaceHasStaticIP(ifaceName string) (ok bool, err error) {
 	filename := fmt.Sprintf("etc/hostname.%s", ifaceName)