Given a sandwich (as a list), return a list of fillings inside the sandwich. This involves ignoring the first and last elements.
get_fillings(["bread", "ham", "cheese", "ham", "bread"]) ➞ ["ham", "cheese", "ham"]
get_fillings(["bread", "sausage", "tomato", "bread"]) ➞ ["sausage", "tomato"]
get_fillings(["bread", "lettuce", "bacon", "tomato", "bread"]) ➞ ["lettuce", "bacon", "tomato"]
The first and last elements will always be "bread".