pidgin/pidgin

Remove the gtk-dnd-hints stuff that should have been removed when we removed dnd from the conversation window.

Testing Done:
Compiled.

Reviewed at https://reviews.imfreedom.org/r/1098/
nullclient = executable('nullclient', 'nullclient.c', 'defines.h',
c_args : ['-DSTANDALONE'],
dependencies : [libpurple_dep, glib])