Fix unnecessary copies in example manifest

[Eriner]

@ahmetb commented in #623 that the copy wildcards are unnecessary

In that case, the tree manifest example should be fixed.

[corneliusweig]

Generally, that's a good idea. However, it needs to be fixed in the right places. For example, the manifest you are referring to, is generated by a template from here https://github.com/ahmetb/kubectl-tree/blob/3f3a78548b3cc3ceb9d06a2d71bda3490db14bf1/.krew.yaml#L24.

[ahmetb]

Yeah. We’ve started enforcing it at some point and a good number of the manifests are autogen’d by krew-release-bot.

Happy to accept PRs to kubectl-tree repo as that’s listed as an example in dev docs.

I wouldn’t bother with others, as we can address them later on when they need manual rev.