Update raspi-config

[nllho]

Some minor updates that came up from poking around in #3094. Think we can close this issue after addressing the main feedback below :)

Incorporate Simon's feedback from #2955 (comment):

• Add warnings to the Advanced Options sections. I borrowed the warning wording from a different part of the docs, if we prefer something else just let me know!
• Specify that it is the Advanced Options may vary across models (GUI options should stay consistent).

Other bits of cleanup for readability:

• Simplify the introduction.
• Make negations easier to read, e.g. 'avoid' instead of 'do not'.

Also proposing that we remove images from this section. To me, they don't seem to be a huge value add, (except for maybe the first image, which could help people confirm they're in the right menu). But let me know if the images here are useful for other reasons :)

[lurch]

I'm not sure this is "correct" as it implies that the GUI version and the terminal version are equivalent, when they're not. The GUI version is much easier to use, but as the now-deleted TIP used to say, there are several advanced options which are available in the CLI tool which aren't available in the GUI tool.
IMHO 🙂

[nathan-contino]

After the code snippet, I would add something like this reduced-size tip admonition:

TIP: Some advanced configuration, including <common example>, is only available in `raspi-config`.

Use your best judgment to determine if there's a decent example worth tossing in there. Personally I think the statement feels a little empty and meaningless without an example -- what kind of 'advanced' config?!?! -- so I lean towards including it if we can come up with one that's short and sweet.

[nathan-contino]

almost LGTM. Just a few minor issues. But I love the fact that we're getting rid of unneeded, hard-to-maintain images, and making this text more consistent. Nice job so far!