Remove in_band_lifetimes from rustc_mir_transform

This one is a heavy `'tcx` user.

Two interesting ones:

This one had the `'tcx` declared on the function, despite the trait taking a `'tcx`:
```diff
-impl Visitor<'_> for UsedLocals {
+impl<'tcx> Visitor<'tcx> for UsedLocals {
     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
```

This one use in-band for one, and underscore for the other:
```diff
-pub fn remove_dead_blocks(tcx: TyCtxt<'tcx>, body: &mut Body<'_>) {
+pub fn remove_dead_blocks<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
```

compiler/rustc_mir_transform/src/nrvo.rs

@@ -165,7 +165,7 @@ struct RenameToReturnPlace<'tcx> {
 }
 
 /// Replaces all uses of `self.to_rename` with `_0`.
-impl MutVisitor<'tcx> for RenameToReturnPlace<'tcx> {
+impl<'tcx> MutVisitor<'tcx> for RenameToReturnPlace<'tcx> {
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
@@ -221,7 +221,7 @@ impl IsReturnPlaceRead {
     }
 }
 
-impl Visitor<'tcx> for IsReturnPlaceRead {
+impl<'tcx> Visitor<'tcx> for IsReturnPlaceRead {
     fn visit_local(&mut self, &l: &Local, ctxt: PlaceContext, _: Location) {
         if l == mir::RETURN_PLACE && ctxt.is_use() && !ctxt.is_place_assignment() {
             self.0 = true;