Deletes an item from a collection, without returning it.
The simplest way to call this function is
(del! coll key). If the index
key is not
present, it's an error.
? special syntax can be used to permit missing items:
(del! coll (? key)).
In that case, the function will succeed even if the index
key is not present.
coll is a deque, slicing syntax is supported:
(del! coll 2 :).
This will delete all elements with an index of 2 or more.
del! is usually more
remove! when deleting a slice, because it doesn't need to perform