cad/freecad: move patch from PATCH_FILES to files/

github's patch file is switching the commit hashes between 11 and
12 digits: see also f4bd9d5c503b508a8d85d2c712acfcf05f1c2f9c, and today
pkg-fallout complained that the patch file was back at it's "original"(?)
format: "size mismatch: expected 34578, actual 34604", log:
http://beefy18.nyi.freebsd.org/data/main-amd64-default/pb6f59eeeccee_s297e9f364b/logs/FreeCAD-0.19.2_3.log
I regret having to put that patch into files/, but that seems better
than to host other project's patches ourselfes.

While here, garbage-collect files/ae641dc5278efaf.patch, which is not
referenced anymore and was applied upstream for FreeCAD 0.19.2.