Remove use-process-group-id flag in plugin

[johscheuer]

What would you like to be added/changed?

In some of our subcommand in the kubectl fdb plugin we have a --use-process-group-id flag but I think we never really used it and everyone is just using the Pod name and the plugin is resolving the process group ID. For simplicity of the code and thee user I think it make sense to remove this option.

[brownleej]

Without this flag, would there be any way to remove a process group that does not have an associated pod?

[johscheuer]

The user could still add it "manually" on the according removal list.