Setup: remove reference to NOOBS

[ghost]

Since NOOBS is now deprecated for end-user installs, remove reference to it from the setup guide.

Also, some other minor fixups to the page, including removing reference to use raspi-config to set the keyboard layout - we've got a GUI setup tool now, and the first run wizard prompts the user for a keyboard layout as well.

[aallan]

I'd encourage you to wrap this PR up in the next week or so as we're in the process of transitioning the documentation from the current Markdown-based source format to Asciidoc. At some point soon — probably around the end of June, beginning of July — we will freeze the current documentation repo. After that time contributions and PRs based on the Markdown source will not be accepted, and any PRs that are still open will be closed.

See #1911 for full details.

[ghost]

This one is ready to integrate.

[aallan]

@lurch You'd looked this one over at one point? Looks good to me, looks good to you?

[ghost]

A bit of background: per Gordon Hollingworth (at #1769 (comment)) NOOBS is no longer the recommended tool for end users. It is however still recommended for resellers to preinstall on SD cards. At #1769 (comment) Gordon also gives his OK to removing documentation for how end users can use NOOBS from the documentation.