fix: remove @workspace from context commands menu

[chungjac]

Problem

@workspace uses vector/semantic search (ONNX + faiss + CodeSage model) has been broken. Even if it is enabled, there are major performance issues with it.

Solution

After checking metrics, we can remove @workspace from the context commands menu so it's no longer shown to users which means that they are not able to use it anymore

Follow up

Dead code cleanup here: #2670

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.25%. Comparing base (73b27f1) to head (8d94e10).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2669   +/-   ##
=======================================
  Coverage   60.25%   60.25%           
=======================================
  Files         279      279           
  Lines       66162    66162           
  Branches     4195     4195           
=======================================
  Hits        39869    39869           
  Misses      26210    26210           
  Partials       83       83           

Flag	Coverage Δ
unittests	60.25% <100.00%> (ø)

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