Remove unneeded #include <epan/prefs.h>; As needed: Add editor-modelines & adjust whitespaxcce.

Change-Id: I6f79357e0f3906f6ccc5b68eb451b69b68636335
Reviewed-on: https://code.wireshark.org/review/3613
Reviewed-by: Bill Meier <wmeier@newsguy.com>