Remove old debugging code

[DavidKutu]

src\client\common\application\debugService.ts
src\client\datascience\jupyterDebugService.ts
src\client\datascience\multiplexingDebugService.ts

This one is still used by interactive window so not sure we can remove it.
src\client\datascience\jupyter\jupyterDebugger.ts

[DonJayamanne]

This will not be done as it was decided (after a team wide discussion) that we'd not change the code as that would require existing users to upgrade ipykernel for debugging of IW after an update.