Remove AWS credential check from cloudwatch output (#3583)

This method is reported to not work with IAM Instance Profiles, and we
do not want to make any calls that would require additional permissions.

(cherry picked from commit 5b40173)

plugins/outputs/cloudwatch/cloudwatch.go

@@ -9,7 +9,6 @@ import (
 
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/service/cloudwatch"
-	"github.com/aws/aws-sdk-go/service/sts"
 
 	"github.com/influxdata/telegraf"
 	internalaws "github.com/influxdata/telegraf/internal/config/aws"
@@ -71,20 +70,7 @@ func (c *CloudWatch) Connect() error {
 		Token:     c.Token,
 	}
 	configProvider := credentialConfig.Credentials()
-
-	stsService := sts.New(configProvider)
-
-	params := &sts.GetSessionTokenInput{}
-
-	_, err := stsService.GetSessionToken(params)
-
-	if err != nil {
-		log.Printf("E! cloudwatch: Cannot use credentials to connect to AWS : %+v \n", err.Error())
-		return err
-	}
-
 	c.svc = cloudwatch.New(configProvider)
-
 	return nil
 }