‘Movie 43’ is brutally unfunny

”This will be ‘Howard the Duck’ for the 21st century,’’ promises the deranged screenwriter (Dennis Quaid) whose very crude sexual ravings provide a tenuous link between the brutally unfunny sketches that comprise “Movie 43.’’ Well, if you mashed-up the worst parts of the infamous “Howard the Duck,’’ “Gigli,’’ “Ishtar’’ and…