Skip checking ipykernel if interpreter has a kernel with kernelspec that has debugger flag set

[DonJayamanne]

THe new ipykernel ends up creating kernlespec.json files with a debugger flag, that only works when a specific version of ipykernel is available in that environment.

I.e. if debugger is available, then ipykernle is available, hence no need to check if ipykernle is installed.

[DonJayamanne]

Testing

• Basically running cells should be faster, when running a cell against an existing kernel for second time.
• YOu can look at the logs if you want to confirm we don't check for ipykernel (in the past we'd have lots indicating we're looking for ipykernle).

FYI - YOu don't need to test this, as its been covered elsewhere, but you can optionally look at the logs if you want to test this