remove post-knative-serving-go-coverage as defaultPostSubmitJobName (k…

…native#644)

We are running code coverage on multiple repos and we are running it not only in pre-submit.
Periodical jobs and post-submit jobs do not need the flag and it is distracting to set the defaultPostSubmitJobName, as it would be printed in logs.

tools/coverage/main.go

@@ -33,7 +33,7 @@ const (
 	defaultStdoutRedirect    = "stdout.txt"
 	defaultCoverageTargetDir = "./pkg/"
 	defaultGcsBucket         = "knative-prow"
-	defaultPostSubmitJobName = "post-knative-serving-go-coverage"
+	defaultPostSubmitJobName = ""
 	defaultCovThreshold      = 80
 )