infra/rdn1edge: reduce the features supported

RD-N1-Edge will henceforth have very minimal updates and test coverage.
So the number of features supported has been reduce to just busybox
boot. Remove all the other features from the list.

Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: I242192904a5176dc2ac7444e0da2d1bfb5637f53