Partial revert of 8d297ec which fixes skirt of second extruder

I remember adding this while thinking "This should probably be better"
but at the time I had no example of processing the secondary skirt/brim.
It turns out that assumption was wrong and I should have restrained
myself from adding code that I couldn't test.

CURA-11718

src/SkirtBrim.cpp

@@ -508,7 +508,7 @@ void SkirtBrim::generateSecondarySkirtBrim(Polygons& covered_area, std::vector<P
             if (first)
             {
                 ref_polys_or_idx = &reference_outline;
-                offset_from_reference = extruder_config.line_width_ / 2 + extruder_config.gap_;
+                offset_from_reference = extruder_config.line_width_ / 2;
             }
             else
             {