[newchem-cpp] cleanup test_status_reporting.cpp

[mabruzzo]

To be reviewed after #469 has been merged

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This does 3 things:

1. it deletes an unused function and some commented-out logic (not sure how I previously let that stuff slip through the cracks)
2. it simplifies a bunch of checks using gmock "matchers" that were enabled by [newchem-cpp] mv grtest machinery into its own subdirectory #469¹
3. it turns on clang-format for test_status_reporting.cpp

Footnotes

1. For added context, googletest was previously being compiled with gmock. In fact the "DEATH TESTS" in this file make use of regex statements to match error messages. The main difference is that we are now using gmock directly ([newchem-cpp] mv grtest machinery into its own subdirectory #469 made this possible by explicitly linking test-code again the gmock library) ↩