Rename Rptr to Ref in AST and HIR

The name makes a lot more sense, and `ty::TyKind` calls it `Ref` already
as well.

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -2657,7 +2657,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             hir::TyKind::Ptr(ref mt) => {
                 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(mt.ty), mutbl: mt.mutbl })
             }
-            hir::TyKind::Rptr(ref region, ref mt) => {
+            hir::TyKind::Ref(ref region, ref mt) => {
                 let r = self.ast_region_to_region(region, None);
                 debug!(?r);
                 let t = self.ast_ty_to_ty_inner(mt.ty, true, false);