test: Use a simple variable to record removed device

test: Use a simple variable to record removed device

At present the entire test state is effective passed into a test driver
just to record which device was removed. This is unnecessary and makes it
harder to track what is going on.

Use a simple boolean instead.

Also drop the unused 'removed' member while we are here.

Signed-off-by: Simon Glass <sjg@chromium.org>