This PR removes three command line parameters from Cloud-enabled Pulumi commands (`update` and `stack init`). Previously we required users to pass in `--organization`, `--repository`, and `--project`. But with the recent "Pulumi repository" changes, we can now get that from the Pulumi workspace. And the project name from the `Pulumi.yaml`.
This PR also fixes a bugs that block the Cloud-enabled CLI path: `update` was getting the stack name via `explicitOrCurrent`, but that fails if the current stack (e.g. the one just initialized in the cloud) doesn't exist on the local disk.
As for better handling of "current stack" and and Cloud-enabled commands, https://github.com/pulumi/pulumi/pull/493 and the PR to enable `stack select`, `stack rm`, and `stack ls` do a better job of handling situations like this.
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