ci: Fix test coverage with codecov

[dplewis]

New Pull Request Checklist

• I am not disclosing a vulnerability.
• I am creating this PR in reference to an issue.

Issue Description

Code coverage has been broken for a while with a number of factors contributing to it. actions/codecov@3.1.0 introduced xcode support. I'm not sure if CODECOV_TOKEN is in the in the repository secrets

https://github.com/codecov/codecov-action/releases/tag/v3.1.0

Approach

• Remove GCC gcov flags
• Enable Clang Coverage (lcov)
• Remove deprecated codecov bash uploader
• Remove codecov.yml in favor of default

TODO

• Update Readme Badge
• Upload CODECOV_TOKEN

[parse-github-assistant]

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[dplewis]

@mtrezza I think it works, I don't have full access to codecov.

https://app.codecov.io/github/parse-community/Parse-SDK-iOS-OSX/commit/f9615fd91c75718a09539f359b85fb138f6e2840/tree

[mtrezza]

I'm not sure if CODECOV_TOKEN is in the in the repository secrets

We don't have a token in the secrets, IIRC that's not necessary.

It seems to work; it's actually a pretty good coverage:

[dplewis]

@mtrezza This is ready for review. Here is what the coverage looks like with everything included

https://app.codecov.io/github/parse-community/Parse-SDK-iOS-OSX/commit/58c9c5be43bb403982effadee84be31d620d18c1/tree

[dplewis]

@mtrezza I made the changes. Can you review it again?

[mtrezza]

Looks good! Thanks for this!

[parseplatformorg]

🎉 This change has been released in version 2.3.0