Remove fixme from test for rust-lang#78 (rust-lang#1868)

Author: zhassan-aws

tests/kani/Vectors/fixme_main.rs renamed to tests/kani/Vectors/sort_by_key.rs

@@ -8,9 +8,8 @@ pub struct GuestRegionMmap {
     guest_base: GuestAddress,
 }
 
-// TODO: running this with --unwrap 2 causes CBMC to hang in propositional reduction.
 #[kani::proof]
-#[kani::unwind(0)]
+#[kani::unwind(3)]
 fn main() {
     let r = GuestRegionMmap { guest_base: GuestAddress(0) };
     let mut regions: Vec<GuestRegionMmap> = vec![];