Drop FileSystem.getRealPath().

[ericsnowcurrently]

(for #8995)

It hasn't been used for a year and a half.

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• [ ] Has a news entry file (remember to thank yourself!)
• Appropriate comments and documentation strings in the code
• [ ] Has sufficient logging.
• [ ] Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated
• [ ] Test plan is updated as appropriate
• [ ] package-lock.json has been regenerated by running npm install (if dependencies have changed)
• [ ] The wiki is updated with any design decisions/details.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities (and 0 Security Hotspots to review)
0 Code Smells

No Coverage information
0.0% Duplication

[codecov-io]

Codecov Report

Merging #9697 into master will increase coverage by 0.14%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #9697      +/-   ##
==========================================
+ Coverage   60.64%   60.79%   +0.14%     
==========================================
  Files         547      550       +3     
  Lines       29541    29651     +110     
  Branches     4467     4485      +18     
==========================================
+ Hits        17914    18025     +111     
+ Misses      10629    10616      -13     
- Partials      998     1010      +12

Impacted Files	Coverage Δ
src/client/common/platform/fileSystem.ts	27.21% <ø> (+0.34%)	⬆️
src/client/common/platform/types.ts	100% <ø> (ø)	⬆️
src/client/common/platform/fs-paths.ts	76.92% <100%> (+4.99%)	⬆️
...ent/common/application/webPanels/webPanelServer.ts	74.64% <0%> (-3.3%)	⬇️
...interpreter/jupyterInterpreterDependencyService.ts	66.05% <0%> (-3.18%)	⬇️
src/client/datascience/jupyter/notebookStarter.ts	66.66% <0%> (-1.91%)	⬇️
...er/jupyterInterpreterSubCommandExecutionService.ts	83.19% <0%> (-0.81%)	⬇️
...rc/client/common/process/pythonExecutionFactory.ts	97.53% <0%> (ø)	⬆️
src/client/interpreter/serviceRegistry.ts	100% <0%> (ø)	⬆️
src/client/datascience/types.ts	100% <0%> (ø)	⬆️
... and 16 more

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