Replace curl with common echtest package

Author: jyyi1

greasereport/main.go

@@ -137,6 +137,7 @@ var curlExitCodeNames = map[int]string{
 }
 
 func runTest(curlPath string, domain tranco.Domain, echGrease bool, maxTime time.Duration) TestResult {
+	// TODO: Refactor this to use internal/echtest.Run to avoid code duplication.
 	result := TestResult{
 		Domain:    domain.Name,
 		Rank:      domain.Rank,