Drop multi-root workspace and dev container support

[brettcannon]

No one was using either, so they were doing nothing but creating prompts that everyone kept dimissing.

[karrtikr]

🎉🎉🎉

[kimadeline]

Can you remove the references to pvsc.code-workspace and .devcontainer/** in .vscodeignore as well please?

[codecov-io]

Codecov Report

Merging #14870 (e87c23a) into main (43d3f8e) will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##            main   #14870   +/-   ##
======================================
  Coverage     65%      65%           
======================================
  Files        551      551           
  Lines      25889    25889           
  Branches    3672     3672           
======================================
  Hits       16902    16902           
  Misses      8294     8294           
  Partials     693      693           

Impacted Files	Coverage Δ
...ent/pythonEnvironments/discovery/locators/index.ts	84% <0%> (-1%)	⬇️
src/client/common/featureDeprecationManager.ts	40% <0%> (ø)
...nt/testing/common/services/discoveredTestParser.ts	15% <0%> (ø)
src/client/telemetry/importTracker.ts	20% <0%> (+1%)	⬆️

[brettcannon]

@kimadeline I just did a clean up of .vscodeignore; PTAL.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65%. Comparing base (43d3f8e) to head (e87c23a).
⚠️ Report is 2720 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff           @@
##            main   #14870   +/-   ##
======================================
  Coverage     65%      65%           
======================================
  Files        551      551           
  Lines      25889    25889           
  Branches    3672     3672           
======================================
  Hits       16902    16902           
  Misses      8294     8294           
  Partials     693      693           

see 4 files with indirect coverage changes

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