Pull request: all: fix lint and naming issues vol. 2

Merge in DNS/adguard-home from 2276-fix-lint-2 to master

Updates #2276.

Squashed commit of the following:

commit 24760b9586bb31be134ef9518dbece485560b1a0
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Dec 7 14:39:50 2020 +0300

    all: fix lint and naming issues vol. 2

internal/dhcpd/nclient4/client.go

@@ -19,9 +19,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"log"
 	"net"
-	"os"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -317,26 +315,6 @@ func WithTimeout(d time.Duration) ClientOpt {
 	}
 }
 
-// WithSummaryLogger logs one-line DHCPv4 message summaries when sent & received.
-func WithSummaryLogger() ClientOpt {
-	return func(c *Client) (err error) {
-		c.logger = ShortSummaryLogger{
-			Printfer: log.New(os.Stderr, "[dhcpv4] ", log.LstdFlags),
-		}
-		return
-	}
-}
-
-// WithDebugLogger logs multi-line full DHCPv4 messages when sent & received.
-func WithDebugLogger() ClientOpt {
-	return func(c *Client) (err error) {
-		c.logger = DebugLogger{
-			Printfer: log.New(os.Stderr, "[dhcpv4] ", log.LstdFlags),
-		}
-		return
-	}
-}
-
 // WithLogger set the logger (see interface Logger).
 func WithLogger(newLogger Logger) ClientOpt {
 	return func(c *Client) (err error) {