platform/arm: drop support for nyan_kitty

Kitty went AUE in M85, and M86 pushed to stable today.

We meet the policies allowed to delete nyan_kitty support from ToT:
https://chromium.googlesource.com/chromiumos/docs/+/master/eol_aue_process.md

BUG=chromium:990438,chromium:1090803
TEST=compiles

Change-Id: I5c29377c93d698e461c34845a6560cfedd1f7ea3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/mosys/+/2469465
Tested-by: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-by: Paul Fagerburg <pfagerburg@chromium.org>
Commit-Queue: Jack Rosenthal <jrosenth@chromium.org>
7 files changed