download_strategy: never verbosely untar

[zmwangx]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew tests with your changes locally?

---

I was responsible for adding the v flag to tar in d7b6230, and I have to admit, I regretted the decision pretty soon. The verbose mode of tar is just too pointlessly verbose. Today I'm finally fed up after having to scroll through this. Let's get rid of it.

[zmwangx]

The verbose mode is especially crazy when you deal with something like boost, where there are 12k+ files in the bottle and you get 800KB+ worth of useless logs in a matter of seconds (~76KB even when gzipped).

[MikeMcQuaid]

I agree. It's also worth noting tar xvf can actually slow down the extraction as it blocks on writing to the terminal.