test: Remove tests violating hardened std::span

[maflcko]

Also, add a test for creating a CScript from an empty byte vector.

To test: rm -rf ./bld-cmake && cmake -B ./bld-cmake -DCMAKE_C_COMPILER='clang' -DCMAKE_CXX_COMPILER='clang++;-stdlib=libc++;-D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_DEBUG' -DBUILD_GUI=OFF -DBUILD_FUZZ_BINARY=OFF -DBUILD_BENCH=OFF -DBUILD_KERNEL_LIB=ON -DENABLE_WALLET=OFF -DENABLE_IPC=OFF && cmake --build ./bld-cmake --parallel $( nproc ) && valgrind --tool=none ./bld-cmake/bin/test_kernel --catch_system_error=no

Before:

/cxx_build/include/c++/v1/span:451: libc++ Hardening assertion __count == 0 || std::to_address(__first) != nullptr failed: passed nullptr with non-zero length in span's constructor (iterator, len)

After: (Passes)

[DrahtBot]

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For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33886.

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ACK	TheCharlatan, stickies-v

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[TheCharlatan]

ACK fadb4f6

[stickies-v]

ACK fadb4f6

It's unfortunate that we can't test the nullptr + non-zero length paths through the c++ wrapper, but removing these cases seems like the best approach for now.