common: unlink remote replicas from set when cow

src/common/set.c

src/test/Makefile

src/test/obj_check_remote/.gitignore

src/test/obj_check_remote/Makefile

src/test/obj_check_remote/TEST0

src/test/obj_check_remote/config.sh

src/test/obj_check_remote/obj_check_remote.c