Pull request: all: imp build tags

Updates #2419.

Squashed commit of the following:

commit e57e6ce56c59d4ef42b1716247fe48a86404179e
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Jun 15 19:37:15 2021 +0300

    all: imp build tags

internal/aghnet/net_darwin.go

@@ -1,6 +1,5 @@
-// +build darwin
-
 //go:build darwin
+// +build darwin
 
 package aghnet
 

internal/aghnet/net_linux.go

@@ -1,6 +1,5 @@
-// +build linux
-
 //go:build linux
+// +build linux
 
 package aghnet
 

internal/aghnet/net_linux_test.go

@@ -1,6 +1,5 @@
-// +build linux
-
 //go:build linux
+// +build linux
 
 package aghnet
 

internal/aghnet/net_others.go

@@ -1,6 +1,5 @@
-// +build !linux,!darwin
-
 //go:build !(linux || darwin)
+// +build !linux,!darwin
 
 package aghnet
 

internal/aghnet/systemresolvers_others.go

@@ -1,6 +1,5 @@
-// +build !windows
-
 //go:build !windows
+// +build !windows
 
 package aghnet
 

internal/aghnet/systemresolvers_others_test.go

@@ -1,6 +1,5 @@
-// +build !windows
-
 //go:build !windows
+// +build !windows
 
 package aghnet
 

internal/aghnet/systemresolvers_windows.go

@@ -1,6 +1,5 @@
-// +build windows
-
 //go:build windows
+// +build windows
 
 package aghnet
 

internal/aghnet/systemresolvers_windows_test.go

@@ -1,6 +1,5 @@
-// +build windows
-
 //go:build windows
+// +build windows
 
 package aghnet