return actual error if failing to update alert data

(cherry picked from commit 36aec52c08)

pkg/api/dashboard.go

@@ -277,10 +277,6 @@ func PostDashboard(c *m.ReqContext, cmd m.SaveDashboardCommand) Response {
 		return Error(500, "Failed to save dashboard", err)
 	}
 
-	if err == m.ErrDashboardFailedToUpdateAlertData {
-		return Error(500, "Invalid alert data. Cannot save dashboard", err)
-	}
-
 	c.TimeRequest(metrics.M_Api_Dashboard_Save)
 	return JSON(200, util.DynMap{
 		"status":  "success",

pkg/api/dashboard_test.go

@@ -727,7 +727,6 @@ func TestDashboardApiEndpoint(t *testing.T) {
 				{SaveError: m.ErrDashboardTitleEmpty, ExpectedStatusCode: 400},
 				{SaveError: m.ErrDashboardFolderCannotHaveParent, ExpectedStatusCode: 400},
 				{SaveError: alerting.ValidationError{Reason: "Mu"}, ExpectedStatusCode: 422},
-				{SaveError: m.ErrDashboardFailedToUpdateAlertData, ExpectedStatusCode: 500},
 				{SaveError: m.ErrDashboardFailedGenerateUniqueUid, ExpectedStatusCode: 500},
 				{SaveError: m.ErrDashboardTypeMismatch, ExpectedStatusCode: 400},
 				{SaveError: m.ErrDashboardFolderWithSameNameAsDashboard, ExpectedStatusCode: 400},