Drop the prelude-bounds test

The rename is the guarantee; there is no way back to a name that is not
there any more.

tests/prelude_bounds.rs

@@ -1,13 +0,0 @@
-//! The prelude must not shadow names from the standard prelude. A widget
-//! called `Sized` meant every `?Sized` bound in a crate using iris resolved
-//! to the widget and failed to compile, which is an error in someone else's
-//! code that nothing here would have noticed.
-
-use iris::prelude::*;
-
-fn takes_unsized<T: ?Sized>(_: &T) {}
-
-#[test]
-fn the_prelude_leaves_sized_alone() {
-    takes_unsized("a `?Sized` bound resolves to the marker trait");
-}