PM / Hibernate: Remove swsusp.c finally

Its contents and entry in Makefile were already removed in
8e60c6a
(Shift remaining code from swsusp.c to hibernate.c)
but somehow it remained in-place (rjw: which most likely was my
mistake).

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Nigel Cunningham <nigel@tuxonice.net>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>