fs/romfs: remove redunant ROMFS_TARGET definition

Probably a leftover from our last fs infra reworking a couple of years
ago.

Incidentally, also added a newline at the end of the file.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>