Remove the STATIC_ASSERT macro from tests where it is unnecessary

[frederick-vs-ja]

For tests only for C++17/20/23, static_assert(expr) can be directly used, and thus it's possibly better to drop STATIC_ASSERT (which possibly slows down the preprocessor).

Also remove STATIC_ASSERT from tests where it's unused.

[StephanTLavavej]

Thanks! Verified that there are no stray changes here by replicating the result of the search-and-replace and diffing them.

It's very rare that static_asserts in tests fail, and if they do, the first thing I do is check the source code, so the fact that MSVC doesn't emit a very detailed diagnostic by default (without /diagnostics:caret, which we stopped bothering with in the test harness) has never annoyed me.

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

Thanks for this significant demacroization! 🧹 🪄 😺