This image is only needed on one device (wAP AC); since this target is
going to be removed anyway it doesn't make sense to add an extra "low
RAM" image.
Fixes OOM issues on RouterBoard wAP AC.
Signed-off-by: Thomas Nixon <tom@tomn.co.uk>
(cherry picked from commit 788c8485eb5b71ef7e7b2a2d3077772e526e9746)