Fix Lite preview CGAL error and remove Full-path adhesive warning

[hazeledmands]

This fixes two small OpenSCAD issues in openGrid.scad.

• Fixes a Lite preview-only CGAL error (The given mesh is not closed! Unable to convert to CGAL_Nef_Polyhedron.) when screw mounting is enabled by replacing the chained attached screw subtraction solids with one explicit unioned cutout shape.
• Removes an unsupported Add_Adhesive_Base named argument from the Full single-tile path. Adhesive backing is a Lite-only feature, and this stray argument produced a warning in the Full preview path.

Repro:

• openscad --preview=throwntogether -o /tmp/preview.png openGrid.scad

Validation:

• Preview mode no longer reports the non-closed mesh error for the default Lite case.
• Preview mode no longer reports the Full-path parameter warning.
• STL export still succeeds with openscad -o /tmp/openGrid.stl openGrid.scad.

History note:

• The Lite adhesive feature was introduced earlier as a Lite-only capability; the unsupported Full-path argument appears to have been introduced later during merge cleanup.