Remove ability to cancel a deployment (for now)

[m--]

We added an attempt to support cancelling deployments in progress, but we need changes on Connect to support it fully. #304 is the issue to fully support this functionality, but in the mean time we should remove what appears to be support for cancellation in Publisher (which doesn't fully work).

Removing this would solve #2179

[dotNomad]

Noting here that we still need the ability to dismiss an in-progress deploy, if we still disable the deploy button while something is in progress. This will prevent a regression of #2057