Screws.scad is now included in core.scad, so doesn't need to be included

anywhere else. utils/core/core.scad is the old version without fasteners to
be used internally in the library.

tests/rails.scad

@@ -17,10 +17,9 @@
 // If not, see <https://www.gnu.org/licenses/>.
 //
 include <../core.scad>
-use <../utils/layout.scad>
-
-include <../vitamins/screws.scad>
 include <../vitamins/rails.scad>
+
+use <../utils/layout.scad>
 use <../vitamins/nut.scad>
 
 sheet = 3;