Remove flink image

[thodson-usgs]

Ideally, the default image should be set in the bakery, and we don't want to override that here:

https://github.com/pangeo-forge/pangeo-forge-runner/blob/e2faa9355bc5f18ebb7e6190462ee860ecafe5cf/pangeo_forge_runner/bakery/flink.py#L217C28-L217C68

pangeo-forge/pangeo-forge-cloud-federation#8 pulls the image from AWS public ECR, which should mitigate the ImagePullBackOff .Error on larger clusters (Once we make this fix to runner)

(you may assign this to me)