docs: Removed redundant lists of supported devices for N Preview

We had several different lists of supported devices. I've removed
them from everywhere <em>but</em> the "Device Images" page; on other
pages, I just say "see Device Images for the list".

See first comment for doc stage location.

bug: 27503340
Change-Id: I4519b7c7064a6cafcfe49f6a30c05d84cdd62eea