Remove comment from hello example

[peterhellberg]

Remove comment in order to reduce the number of wasted lines in https://go.dev/play/
(The current design shows fewer lines of code than the old version of the playground)

Users would otherwise have to manually remove these each time they want to share a snippet on the playground.

[peterhellberg]

Signed the CLA after opening the PR.

[dolmen]

I think that the comment is in fact useful for new comers. It might also be useful when sending a Playground link (after code edit) to someone else, so this would not be a problem to many people who start from this example.

I have much concerns about the screen space wasted with the new UI of the Go Playground (2 third of screen wasted on desktop to show other things than the code) but the example code is not a problem from my point of view.

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