Rename HandlerInner::delay_span_bug as HandlerInner::span_delayed_bug.

Because the corresponding `Level` is `DelayedBug` and `span_delayed_bug`
follows the pattern used everywhere else: `span_err`, `span_warning`,
etc.

compiler/rustc_passes/src/liveness.rs

@@ -592,7 +592,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
         match self.successors[ln] {
             Some(successor) => self.assigned_on_entry(successor, var),
             None => {
-                self.ir.tcx.sess.delay_span_bug(DUMMY_SP, "no successor");
+                self.ir.tcx.sess.span_delayed_bug(DUMMY_SP, "no successor");
                 true
             }
         }