Use pybind11 type caster for GCAgg.clippath

Now that everything else is using pybind11, this works without issue.

Author: QuLogic

src/py_converters_11.h

@@ -294,8 +294,7 @@ namespace PYBIND11_NAMESPACE { namespace detail {
             value.join = src.attr("_joinstyle").cast<agg::line_join_e>();
             value.dashes = src.attr("get_dashes")().cast<Dashes>();
             value.cliprect = src.attr("_cliprect").cast<agg::rect_d>();
-            /* value.clippath = src.attr("get_clip_path")().cast<ClipPath>(); */
-            convert_clippath(src.attr("get_clip_path")().ptr(), &value.clippath);
+            value.clippath = src.attr("get_clip_path")().cast<ClipPath>();
             value.snap_mode = src.attr("get_snap")().cast<e_snap_mode>();
             value.hatchpath = src.attr("get_hatch_path")().cast<mpl::PathIterator>();
             value.hatch_color = src.attr("get_hatch_color")().cast<agg::rgba>();