* nomad/structs/csi: delete just one plugin type from a node
* nomad/structs/csi: add DeleteAlloc
* nomad/state/state_store: add deleteJobFromPlugin
* nomad/state/state_store: use DeleteAlloc not DeleteNodeType
* move CreateTestCSIPlugin to state to avoid an import cycle
* nomad/state/state_store_test: delete a plugin by deleting its jobs
* nomad/*_test: move CreateTestCSIPlugin to state
* nomad/state/state_store: update one plugin per transaction
* command/plugin_status_test: move CreateTestCSIPlugin
* nomad: csi: handle nils CSIPlugin methods, clarity
