Remove old Cairo render method that has been replaced.
Fix bug #461: Handles priorities are not working in some cases.
The root cause of the bug comes from a commit that allows reverse manipulation of the width handles under bone influence. Width handles needs to calculate the position of the origin duck to be placed correctly. The Duck::get_sub_trans_origin member retrieves the untransformed position of the origin handle (when it exists) of the handle in question (the width handle in the commit). Originally this member was just  returning the sub_trans_position of the origin duck but since the inclusion of the bones, the way to calculate the untransformed position of the origin handle based on the origin handle is to obtain the transformed position of the origin handle and apply the untransformation stack of the current handle being positioned (that should be the same than its origin handle). That transformation and later another untransformation (that should give the origin duck original value) produces one rounding error. That rounding error is carried on until the final Duck::get_trans_point used in the Duck::find_duck where the handle priorities is performed.
See https://github.com/synfig/synfig/commit/1efad88f9d2a8855df740e014f2cd00ce04502b4
Reversing that part of the previous mentioned commit, fixes the bug but produces that the width duck under bone influence are wrongly placed.

So the only way to fix this and keep the functionality is to do not expect that the handles were exactly on the same place but very close and that's what I did.