CloudWatch: Add test to executeStartQuery (#45888)

* CloudWatch: Add test to executeStartQuery

* Add test for absence of limit

* Restrict assertions to limit in some tests

pkg/tsdb/cloudwatch/annotation_query_test.go

@@ -97,10 +97,3 @@ func TestQuery_AnnotationQuery(t *testing.T) {
 		}, client.calls.describeAlarms[0])
 	})
 }
-
-func pointerString(s string) *string {
-	return &s
-}
-func pointerInt64(i int64) *int64 {
-	return &i
-}