content: clean up slice of slices code example

The variable represents a board, not a game.

Also, there's no point in creating a helper function to print
the board, since it's only printed once.

Change-Id: I34897302d80d0aa8de63a424f570c39f64fa6538
Reviewed-on: https://go-review.googlesource.com/19400
Reviewed-by: Andrew Gerrand <adg@golang.org>
1 file changed