Chore: Upgrade to Go 1.13 (#19502)

* Chore: Upgrade to Go 1.13

Fixes: #18878

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>

* Chore: Upgrade lint tools in order to work with Go 1.13

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>

* Chore: Fix Go linting issues

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>

pkg/tsdb/elasticsearch/elasticsearch.go

@@ -4,17 +4,15 @@ import (
 	"context"
 	"fmt"
 
-	"github.com/grafana/grafana/pkg/infra/log"
 	"github.com/grafana/grafana/pkg/models"
 	"github.com/grafana/grafana/pkg/tsdb"
-	"github.com/grafana/grafana/pkg/tsdb/elasticsearch/client"
+	es "github.com/grafana/grafana/pkg/tsdb/elasticsearch/client"
 )
 
 // ElasticsearchExecutor represents a handler for handling elasticsearch datasource request
 type ElasticsearchExecutor struct{}
 
 var (
-	glog               log.Logger
 	intervalCalculator tsdb.IntervalCalculator
 )
 
@@ -24,7 +22,6 @@ func NewElasticsearchExecutor(dsInfo *models.DataSource) (tsdb.TsdbQueryEndpoint
 }
 
 func init() {
-	glog = log.New("tsdb.elasticsearch")
 	intervalCalculator = tsdb.NewIntervalCalculator(nil)
 	tsdb.RegisterTsdbQueryEndpoint("elasticsearch", NewElasticsearchExecutor)
 }