remove special handling of ipython_kernel in launcher

- set JPY_PARENT_PID and JPY_INTERRUPT_EVENT env variables for all kernels
- no custom kernel args other that console passthrough
- use devnull instead of `--no-stdout` (comments claim it shouldn't work, but tests suggest it does, so let's keep an eye on this)

closes #7085
Eh, I just filtered my way right through it. Nothing on GitHub (since Calico is on BitBucket).

[Google results just turn up IPython and Calico](https://www.google.com/search?q=IPY_INTERRUPT_EVENT).