build-image: clean out deleted loop mappings
/dev/loop0 will fail losetup if it doesn't get cleaned out
Signed-off-by: Angus Ainslie (Purism) angus@akkea.ca
/dev/loop0 will fail losetup if it doesn't get cleaned out
Signed-off-by: Angus Ainslie (Purism) angus@akkea.ca