Pull request:* all: fix all staticcheck simplification and unused warnings

Merge in DNS/adguard-home from 2270-fix-s-u-warnings to master

Squashed commit of the following:

commit 03e0f78bd471057007c2d4042ee26eda2bbc9b29
Merge: 50dc3ef5c 7e16fda57
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Nov 6 11:54:09 2020 +0300

    Merge branch 'master' into 2270-fix-s-u-warnings

commit 50dc3ef5c44a5fdc941794c26784b0c44d7b5aa0
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Nov 5 19:48:54 2020 +0300

    * all: improve code quality

commit d6d804f759ce3e47154a389b427550e72c4b9090
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Nov 5 18:03:35 2020 +0300

    * all: fix all staticcheck simplification and unused warnings

    Closes #2270.

internal/home/memory.go

@@ -32,13 +32,9 @@ func memoryUsage(args options) {
 	// that the OS could reclaim the free memory
 	go func() {
 		ticker := time.NewTicker(5 * time.Minute)
-		for {
-			select {
-			case t := <-ticker.C:
-				t.Second()
-				log.Debug("Free OS memory")
-				debug.FreeOSMemory()
-			}
+		for range ticker.C {
+			log.Debug("free os memory")
+			debug.FreeOSMemory()
 		}
 	}()
 }