Normalize commandline in media resource tests (#20118)

## Summary of the Pull Request
Some of the Media Resource tests were failing on my machine. Turns out
that it's because my machine uses `C:\WINDOWS` instead of `C:\Windows`.

This PR fixes those tests by calling `Profile::NormalizeCommandline()`
on a few impacted strings. This also makes them loaded after enabling
filesystem redirection in `TEST_CLASS_SETUP` so that we resolve to the
correct path expected by x86.

Admittedly, I'm not the biggest fan of using that to fix the tests, but
it's better than the alternative which is a case-insensitive string
comparison. Also, the tests are testing fallback behavior, so this
doesn't really impact that. It just makes the tests more consistently
reliable.

This also removes the unused `pingCommandline` variable.

## Validation Steps Performed
✅ Tests pass