chore: change nsis script to use global cmd.exe @W-19315214@

[WillieRuemmele]

What does this PR do?

changes the custom nsis used in sf for checking for installed sfdx CLI to use the global cmd.exe instead of a local, possibly malicious cmd.exe file

Acceptance Criteria

Testing Notes

oh boi - needs a windows machine
needs oclif/oclif#1852

setup:
(I had to delete the JIT section in pjson in CLI for some steps to work locally)

1. be on windows
2. checkout the oclif PR / yarn / yarn build
3. checkout this PR / yarn /
4. run oclif pack:tarballs --xz --parallel --prune-lockfiles --targets win32-x64 or whatever windows target you need (just builds one, instead of every, installer)
5. ../path/to/oclif/bin/run.js pack:win --prune-lockfiles --targets win32-x64 --defender-exclusion unchecked
6. If step 6 fails, there's a good chance it was at least able to build the .nsi file. I believe this file is in the output, and it's in tmp/. You can makensis path/to/.nsi which will compile your .nsi into a .exe, you can then drag that .exe into your testing folder
7. drag the new built installer from dist/ to your directory with a "malicious" cmd.exe program in it and install

Notes:
sometimes the pack:win command would fail, but I'd still get the required sf.nsi file, which then I'd have to run makensis path/to/sf.nsi which would build the installer

Checklist

• This change has been approved by the CLI Review Board or approval isn't required. Anything that adds/changes/deletes commands, flags, output, or json output has to be reviewed.
• Does this follow the deprecation policy?

What issues does this PR fix or reference?

@W-19315214@