Delete multiple AltTesterPrefab before building app

[RobertPoienar]

In the pipeline script when we build the instrumented app we adding an AltTesterPrefab without checking if the scene already has a prefab in it. This could cause issue because we only add instrumentation setting only to one and could cause issue with connection settings.

As a solution just delete all the AltTesterPrefab from the scene before adding the one we want