Stop enabling in_band_lifetimes in rustc_data_structures

There's a conversation in the tracking issue about possibly unaccepting `in_band_lifetimes`, but it's used heavily in the compiler, and thus there'd need to be a bunch of PRs like this if that were to happen.

So here's one to see how much of an impact it has.

(Oh, and I removed `nll` while I was here too, since it didn't seem needed.  Let me know if I should put that back.)

compiler/rustc_data_structures/src/graph/vec_graph/mod.rs

@@ -94,7 +94,7 @@ impl<N: Idx> WithNumEdges for VecGraph<N> {
     }
 }
 
-impl<N: Idx> GraphSuccessors<'graph> for VecGraph<N> {
+impl<'graph, N: Idx> GraphSuccessors<'graph> for VecGraph<N> {
     type Item = N;
 
     type Iter = std::iter::Cloned<std::slice::Iter<'graph, N>>;