cnp: change drag win type to ELM_WIN_DND
cnp: change drag win type to ELM_WIN_DND

Summary:
Drag win should use ELM_WIN_DND.
The drag win in _drag_start function was added when ELM_WIN_DND
was not supported. Now we have ELM_WIN_DND, drag win needs to
change to ELM_WIN_DND.

@fix

Reviewers: JackDanielZ, cedric, Hermet

Subscribers: seoz

Differential Revision: https://phab.enlightenment.org/D2784

rvandegrift/elementary,tasn/elementary,rvandegrift/elementary,tasn/elementary,rvandegrift/elementary,tasn/elementary,FlorentRevest/Elementary,FlorentRevest/Elementary,FlorentRevest/Elementary,tasn/elementary,tasn/elementary,rvandegrift/elementary,FlorentRevest/Elementary