test: Remove system_tests/run_command runtime dependencies #33929

1. 
   hebasto commented at 11:03 pm on November 23, 2025: member

   system_tests currently rely on the presence of cat, echo, false and sh in PATH at runtime.

   This PR:

   1. Removes these dependencies.
   2. Eliminates all but one platform-specific code paths.
2. test: Remove `system_tests/run_command` runtime dependencies a4144ac1d6
3. test: Enable `system_tests/run_command` "stdin" test on Windows c996515a6d
4. hebasto added the label Tests on Nov 23, 2025
5. 
   DrahtBot commented at 11:03 pm on November 23, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33929.

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   Conflicts

   Reviewers, this pull request conflicts with the following ones:

   • #33483 (CMake: Add dynamic test discovery by purpleKarrot)

   If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

Contributors
hebasto DrahtBot

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Tests