Remove frontend.h C++ header tests

[dkorpel]

They have been superseded by ./build.d cpp-layout-test #23187

Depends on #23190

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

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[ibuclaw]

@dkorpel nonblocking question.

Does this python script allow checking multiple targets?

• Windows/MSVC (different mangling scheme)
• x86/«any other arch»32 (different pointer size)
• ARM64/PPC64 (different c_real size)
• Darwin/PPC32 (different c_bool size)

[dkorpel]

Currently the script uses clang to walk all headers to generate a single .d file with mangles and offsets hard-coded for Linux 64-bit:

https://gist.github.com/dkorpel/c80efc25b1b493a5079e695b39c6195f

But the script could be edited to use whatever configurations clang supports, and invoked multiple times to generate different variants.

[thewilsonator]

Dependant PR merged