This also removes some tests which were redundant, wrong, or never run.
Specifically,
- `libcxx/utilities/meta/stress_tests/*` were never run and are of
questionable usefulness
- `libcxx/utilities/template.bitset/includes.pass.cpp` is completely
redundant and partially incorrect
Also notably,
`libcxx/language.support/support.c.headers/support.c.headers.other/math.lerp.verify.cpp`
has been refactored to only test the standard mandate.
3ca414b63a