Cleaning Up VCR Specs

Dropped all cases of VCR.use_cassette in favour of RSpec metadata.

Now we can just use:

```
describe SomeClass, :vcr do
  ...
  ...
end
```

See <https://relishapp.com/vcr/vcr/v/2-9-2/docs/test-frameworks/usage-with-rspec-metadata> for more info.