Remove comment from hello example

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.

_content/doc/play/hello.go

@@ -1,5 +1,3 @@
-// You can edit this code!
-// Click here and start typing.
 package main
 
 import "fmt"