Remove obsolete test

This test no longer makes sense with classes instead of resources,
since class types can't be dereferenced.

src/test/compile-fail/borrowck-assign-to-resource.rs

@@ -1,6 +0,0 @@
-resource r(_r: int) {}
-
-fn main() {
-    let x = r(3);
-    *x = 4; //! ERROR assigning to resource content
-}