Reworked the "new" bridging to respect the bridge_flow_ratio

by maintaining extrusion spacing, but modifying the extrusion width
and / or height.

xs/xsp/Flow.xsp

@@ -16,8 +16,6 @@
     float nozzle_diameter();
     bool bridge();
     float spacing();
-    float spacing_to(Flow* other)
-        %code{% RETVAL = THIS->spacing(*other); %};
     int   scaled_width();
     int   scaled_spacing();
     double mm3_per_mm();