coll: replace submodule json-c

[hzhou]

Pull Request Description

We do not require arbitrary JSON support for parsing collective tuning file, thus we can easily roll a custom parser. This removes the dependency on json-c and potentially is more robust due to much less code.

• [ ] add unit tests to ensure robust support for all potential JSON-conforming inputs

Author Checklist

• [x] Provide Description Particularly focus on why, not what. Reference background, issues, test failures, xfail entries, etc.
• [x] Commits Follow Good Practice Commits are self-contained and do not do two things at once. Commit message is of the form: module: short description Commit message explains what's in the commit.
• [x] Passes All Tests Whitespace checker. Warnings test. Additional tests via comments.
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[hzhou]

test:mpich/ch3/most