Testing followup for P0722R3 Destroying delete

[CaseyCarter]

We can't complete activation of test coverage for destroying delete until an MSVC that implements the feature ships. This should be Visual Studio 2019 16.7 Preview 2. When that release ships:

• Disable skips annotated "C++20 P0722R3 "Efficient sized delete for variable sized classes" in libc++'s skipped_tests.txt and expected_results.txt

• Update the feature-test macro test bits that mention "VS 2019 16.7p1" (Yes, p1, despite that the compiler feature is actually in Preview 2.)

[StephanTLavavej]

@CaseyCarter Does this need Preview 1 or Preview 2?

[CaseyCarter]

@CaseyCarter Does this need Preview 1 or Preview 2?

It's actually Preview 2 (I've clarified the first post a bit).