remove stop button

[DavidKutu]

For #6904 and #6860

To stop, users can click the stop cell button on the left.

• 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).

[codecov-commenter]

Codecov Report

Merging #7138 (c49bdec) into main (b7d582c) will increase coverage by 0%.
The diff coverage is n/a.

@@          Coverage Diff          @@
##            main   #7138   +/-   ##
=====================================
  Coverage     64%     64%           
=====================================
  Files        362     362           
  Lines      22902   22897    -5     
  Branches    3435    3434    -1     
=====================================
+ Hits       14850   14855    +5     
+ Misses      6737    6729    -8     
+ Partials    1315    1313    -2     

Impacted Files	Coverage Δ
src/client/datascience/constants.ts	99% <ø> (-1%)	⬇️
src/client/debugger/jupyter/debuggingManager.ts	28% <ø> (+<1%)	⬆️
...lient/datascience/variablesView/notebookWatcher.ts	83% <0%> (-3%)	⬇️
src/client/datascience/baseJupyterSession.ts	63% <0%> (-1%)	⬇️
src/client/datascience/jupyter/kernelVariables.ts	45% <0%> (+<1%)	⬆️
...t/datascience/notebook/vscodeNotebookController.ts	79% <0%> (+1%)	⬆️
.../datascience/notebook/notebookControllerManager.ts	86% <0%> (+1%)	⬆️
src/client/common/cancellation.ts	76% <0%> (+4%)	⬆️