Pull request:* all: fix all staticcheck SA warnings

Merge in DNS/adguard-home from 2238-fix-static-analisys-warnings to master

Squashed commit of the following:

commit 721ca6fa1cbfdfe9d414e6ed52fec4a64653fb52
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Oct 30 15:48:10 2020 +0300

    * all: fix all staticcheck SA warnings

    Closes #2238.

internal/querylog/decode_test.go

@@ -15,7 +15,7 @@ func TestJSON(t *testing.T) {
 	assert.Equal(t, "keystr", k)
 	assert.Equal(t, "val", v)
 
-	k, v, jtype = readJSON(&s)
+	k, _, jtype = readJSON(&s)
 	assert.Equal(t, jtype, int32(jsonTObj))
 	assert.Equal(t, "obj", k)
 
@@ -29,6 +29,6 @@ func TestJSON(t *testing.T) {
 	assert.Equal(t, "keyint", k)
 	assert.Equal(t, "123456", v)
 
-	k, v, jtype = readJSON(&s)
+	_, _, jtype = readJSON(&s)
 	assert.True(t, jtype == jsonTErr)
 }