Revert "use Win32 file APIs and widePath for file ops to support long filenames"

[bnbarham]

Reverts #1004. Possibly the cause of Windows CI failures, will run cross PR testing to check.

[bnbarham]

@swift-ci please test

[bnbarham]

https://ci-external.swift.org/job/swift-PR-windows/44372/ is the swift cross-pr testing run. Though I'm not sure how they could be different 🤔

[bnbarham]

Going to merge this to unblock CI. Note that from what I can see in the logs, the PR testing in the original job didn't actually test the change:

Checking out Revision f36582cf601212160fdde492ae5b17b2846f2030 (refs/remotes/origin/pr/1004/merge)
 > git config core.sparsecheckout # timeout=10
 > git checkout -f f36582cf601212160fdde492ae5b17b2846f2030 # timeout=10
Commit message: "Merge bb4eef80525011a5a3d3153d881b543746926d8d into 5891ce06197da2ed99099bf82c389eab6fdc0fd9"
...
update-checkout succeeded
...
llbuild                            : 5891ce06197da2ed99099bf82c389eab6fdc0fd9

Will look into that separately.