Remove ordering traits from rustc_borrowck::constraints::OutlivesConstraint

In two cases where this ordering was used, I've replaced the sorting
to use a key that does not include DefId. I'm not sure this is correct
in terms of our goals from #90317, or otherwise.

compiler/rustc_borrowck/src/constraints/mod.rs

@@ -72,7 +72,7 @@ fn index(&self, i: OutlivesConstraintIndex) -> &Self::Output {
     }
 }
 
-#[derive(Clone, PartialEq, Eq, PartialOrd, Ord)]
+#[derive(Clone, PartialEq, Eq)]
 pub struct OutlivesConstraint<'tcx> {
     // NB. The ordering here is not significant for correctness, but
     // it is for convenience. Before we dump the constraints in the

compiler/rustc_borrowck/src/region_infer/dump_mir.rs

@@ -72,7 +72,7 @@ fn for_each_constraint(
         }
 
         let mut constraints: Vec<_> = self.constraints.outlives().iter().collect();
-        constraints.sort();
+        constraints.sort_by_key(|c| (c.sup, c.sub));
         for constraint in &constraints {
             let OutlivesConstraint { sup, sub, locations, category, variance_info: _ } = constraint;
             let (name, arg) = match locations {

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -612,7 +612,7 @@ pub(super) fn solve(
     fn propagate_constraints(&mut self, _body: &Body<'tcx>) {
         debug!("constraints={:#?}", {
             let mut constraints: Vec<_> = self.constraints.outlives().iter().collect();
-            constraints.sort();
+            constraints.sort_by_key(|c| (c.sup, c.sub));
             constraints
                 .into_iter()
                 .map(|c| (c, self.constraint_sccs.scc(c.sup), self.constraint_sccs.scc(c.sub)))