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/function_item_references.rs

@@ -27,7 +27,7 @@ struct FunctionItemRefChecker<'a, 'tcx> {
     body: &'a Body<'tcx>,
 }
 
-impl<'a, 'tcx> Visitor<'tcx> for FunctionItemRefChecker<'a, 'tcx> {
+impl<'tcx> Visitor<'tcx> for FunctionItemRefChecker<'_, 'tcx> {
     /// Emits a lint for function reference arguments bound by `fmt::Pointer` or passed to
     /// `transmute`. This only handles arguments in calls outside macro expansions to avoid double
     /// counting function references formatted as pointers by macros.
@@ -92,7 +92,7 @@ impl<'a, 'tcx> Visitor<'tcx> for FunctionItemRefChecker<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> FunctionItemRefChecker<'a, 'tcx> {
+impl<'tcx> FunctionItemRefChecker<'_, 'tcx> {
     /// Emits a lint for function reference arguments bound by `fmt::Pointer` in calls to the
     /// function defined by `def_id` with the substitutions `substs_ref`.
     fn check_bound_args(