Remove google_protos and update protobuf to 0.14

[eliasdarruda]

Closes #42

[mjheilmann]

It appears that the CI configuration isn't at 100% and isn't letting me trigger it here, but I ran several checks locally:

• mix test on the library application fails
• mix deps.get in examples/helloworld fails, there is a dependency collision from the main library
• when examples/helloworld is updated so mix dips.get succeeds, its mix test fails

A friendly reminder here to also check your PR locally and run tests when drafting PRs, you could have discovered some of these issues directly.

This PR is doing 2 separate actions and each have their own complexities. I request that you split this PR into two PRs so we can carefully ensure each change is in a good and mergable state.

Removing google_protos

This library relies on google_protos for its unit tests. Just removing the library without other changes causes multiple test cases to fail. The protobuf library performs a hack to have the definitions available for its own tests without depending on it explicitly. This dependency was added in #26

Updating protobuf from 0.12 to 0.14

There are breaking changes in this upgrade. These are visible through the examples/helloworld unit tests. php_generic_services is in use but appears to be removed, but the example also fails to reflect for additional reasons that I haven't dug into.

As an aside, having unit tests in the examples folder that cover different behaviors from the main library seems problematic, but I don't know that it's not simply failing for related reasons. I am interested if there are other issues lurking in this upgrade, or if there are simply flaws in the example and its tests.

[eliasdarruda]

My bad on not testing, the reason it is failing is because the compiled google protos from the protobuf package does not include the descriptor.

I've opened elixir-protobuf/protobuf#401 to track that. The concern here is that any package that depends on this lib cannot upgrade to the newest elixir-protobuf version because of this breaking change.

Once that is addressed there I'll revisit the tests here