MM-36764 mlog refactor (#18118)

Refactor mlog
- simplify mlog by removing redundant code
- remove Zap dependency
- update unit test helpers
- update logging config
- update auditing

services/slackimport/main_test.go

@@ -7,8 +7,6 @@ import (
 	"fmt"
 	"os"
 	"testing"
-
-	"github.com/mattermost/mattermost-server/v6/shared/mlog"
 )
 
 func TestMain(m *testing.M) {
@@ -22,8 +20,6 @@ func TestMain(m *testing.M) {
 		panic(fmt.Sprintf("Failed to set current working directory to %s: %s", "../..", err.Error()))
 	}
 
-	mlog.DisableZap()
-
 	defer func() {
 		err := os.Chdir(prevDir)
 		if err != nil {