Revert all the FS-related changes.

[ericsnowcurrently]

(for #8890)

We continue to have problems due to the FS-related changes. So I'm reverting them until we can get all that sorted out.

[codecov-io]

Codecov Report

Merging #8970 into master will decrease coverage by 0.26%.
The diff coverage is 38.86%.

@@            Coverage Diff             @@
##           master    #8970      +/-   ##
==========================================
- Coverage   58.17%   57.91%   -0.27%     
==========================================
  Files         529      530       +1     
  Lines       27729    27638      -91     
  Branches     4178     4182       +4     
==========================================
- Hits        16132    16006     -126     
- Misses      10705    10739      +34     
- Partials      892      893       +1

Impacted Files	Coverage Δ
src/client/sourceMapSupport.ts	81.25% <ø> (ø)	⬆️
src/client/common/platform/types.ts	100% <ø> (ø)	⬆️
...rc/client/debugger/debugAdapter/serviceRegistry.ts	0% <0%> (ø)	⬆️
.../datascience/interactive-common/interactiveBase.ts	18.67% <0%> (ø)	⬆️
src/client/providers/renameProvider.ts	22.72% <0%> (-0.68%)	⬇️
...rpreter/locators/services/baseVirtualEnvService.ts	28.3% <0%> (ø)	⬆️
src/client/providers/jediProxy.ts	23.42% <100%> (+0.05%)	⬆️
src/client/workspaceSymbols/provider.ts	93.33% <100%> (ø)	⬆️
src/client/common/net/fileDownloader.ts	100% <100%> (ø)	⬆️
src/client/common/variables/environment.ts	92.3% <100%> (-0.1%)	⬇️
... and 19 more

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[ericsnowcurrently]

The failing smoke test does not appear to be related. I've opened a separate issue about that failure: #8984.