Make clean work when a recipe has no recipe.sh.
Make clean work when a recipe has no recipe.sh.

Previously, one had to have a recipe.sh in all recipe directories in
order to run `make clean` successfully. This fixes that.

Signed-off-by: Wren Turkal <1c01a65c7a4125e8293dc90f61316d18ba72756a@penguintechs.org>

redox-os/cookbook,redox-os/cookbook,redox-os/cookbook,redox-os/cookbook