Use 'mir lifetime name more.

Some types have a `body: &'mir Body<'tcx>` and some have `body: &'a
Body<'tcx>`. The former is more readable, so this commit converts some
fo the latter to the former.

compiler/rustc_mir_dataflow/src/framework/direction.rs

@@ -287,12 +287,12 @@ impl Direction for Backward {
     }
 }
 
-struct BackwardSwitchIntEdgeEffectsApplier<'a, 'tcx, D, F> {
-    body: &'a mir::Body<'tcx>,
+struct BackwardSwitchIntEdgeEffectsApplier<'mir, 'tcx, D, F> {
+    body: &'mir mir::Body<'tcx>,
     pred: BasicBlock,
-    exit_state: &'a mut D,
+    exit_state: &'mir mut D,
     bb: BasicBlock,
-    propagate: &'a mut F,
+    propagate: &'mir mut F,
     effects_applied: bool,
 }
 
@@ -523,9 +523,9 @@ impl Direction for Forward {
     }
 }
 
-struct ForwardSwitchIntEdgeEffectsApplier<'a, D, F> {
-    exit_state: &'a mut D,
-    targets: &'a SwitchTargets,
+struct ForwardSwitchIntEdgeEffectsApplier<'mir, D, F> {
+    exit_state: &'mir mut D,
+    targets: &'mir SwitchTargets,
     propagate: F,
 
     effects_applied: bool,