Remove Disabled, Duplicate and Library-Only Unit Tests

Delete test cases that never run (#if 0 blocks, [NotWorking] cases, commented-out Perl ports, blocks behind undefined macros), cases that cannot fail, cases that only exercise boost::polygon directly, and cases whose assertions another test already makes on the same path. Remove the helpers, includes and fixture only those cases used.

tests/fff_print/test_flow.cpp

@@ -58,23 +58,6 @@ SCENARIO("Flow math for non-bridges", "[Flow]") {
             }
         }
     }
-
-#if 0
-    /// Check for an edge case in the maths where the spacing could be 0; original
-    /// math is 0.99. Slic3r issue #4654
-    GIVEN("Input spacing of 0.414159 and a total width of 2") {
-        double in_spacing = 0.414159;
-        double total_width = 2.0;
-        auto flow = Flow::new_from_spacing(1.0, 0.4, 0.3);
-        WHEN("solid_spacing() is called") {
-            double result = flow.solid_spacing(total_width, in_spacing);
-            THEN("Yielded spacing is greater than 0") {
-                REQUIRE(result > 0);
-            }
-        }
-    }
-#endif    
-
 }
 
 /// Spacing, width calculation for bridge extrusions