Pub/Sub: Remove `PleaseIgnoreThisSimplifiesTestingTheSamples` from streaming pull samples

[kamalaboulhosn]

Several of the Pub/Sub streaming pull samples have a call that looks like PleaseIgnoreThisSimplifiesTestingTheSamples(). As I understand it, this is to help with the continuous tests on the samples. However, C++ is the only language that has this and I think it complicates the sample. We should look for a way to remove this.

[scotthart]

We'll see if we can make this prettier.