Pull request 2048: AG-26594-fix-filtering-race

Squashed commit of the following:

commit 9b5b035aa3edfe20cbc26772b8a5c76d81288116
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Fri Oct 20 13:00:29 2023 +0300

    filtering: imp code

commit 406f4015d80d8b11fbd0aeacfabe686931bbe3fb
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Thu Oct 19 15:04:13 2023 +0300

    filtering: fix race

internal/filtering/filter.go

@@ -263,30 +263,6 @@ func assignUniqueFilterID() int64 {
 	return value
 }
 
-// Sets up a timer that will be checking for filters updates periodically
-func (d *DNSFilter) periodicallyRefreshFilters() {
-	const maxInterval = 1 * 60 * 60
-	ivl := 5 // use a dynamically increasing time interval
-	for {
-		isNetErr, ok := false, false
-		if d.conf.FiltersUpdateIntervalHours != 0 {
-			_, isNetErr, ok = d.tryRefreshFilters(true, true, false)
-			if ok && !isNetErr {
-				ivl = maxInterval
-			}
-		}
-
-		if isNetErr {
-			ivl *= 2
-			if ivl > maxInterval {
-				ivl = maxInterval
-			}
-		}
-
-		time.Sleep(time.Duration(ivl) * time.Second)
-	}
-}
-
 // tryRefreshFilters is like [refreshFilters], but backs down if the update is
 // already going on.
 //