Simplify calls to tcx.mk_const

`mk_const(ty::ConstKind::X(...), ty)` can now be simplified to
`mk_cosnt(...,                   ty)`.

I searched with the following regex: \mk_const\([\n\s]*(ty::)?ConstKind\
I've left `ty::ConstKind::{Bound, Error}` as-is, they seem clearer this
way.

compiler/rustc_middle/src/mir/mod.rs

@@ -2527,8 +2527,7 @@ impl<'tcx> ConstantKind<'tcx> {
                 let generics = tcx.generics_of(item_def_id);
                 let index = generics.param_def_id_to_index[&def_id];
                 let name = tcx.item_name(def_id);
-                let ty_const =
-                    tcx.mk_const(ty::ConstKind::Param(ty::ParamConst::new(index, name)), ty);
+                let ty_const = tcx.mk_const(ty::ParamConst::new(index, name), ty);
                 debug!(?ty_const);
 
                 return Self::Ty(ty_const);

compiler/rustc_middle/src/ty/consts.rs

@@ -76,10 +76,10 @@ impl<'tcx> Const<'tcx> {
         match Self::try_eval_lit_or_param(tcx, ty, expr) {
             Some(v) => v,
             None => tcx.mk_const(
-                ty::ConstKind::Unevaluated(ty::UnevaluatedConst {
+                ty::UnevaluatedConst {
                     def: def.to_global(),
                     substs: InternalSubsts::identity_for_item(tcx, def.did.to_def_id()),
-                }),
+                },
                 ty,
             ),
         }
@@ -134,7 +134,7 @@ impl<'tcx> Const<'tcx> {
                 let generics = tcx.generics_of(item_def_id);
                 let index = generics.param_def_id_to_index[&def_id];
                 let name = tcx.item_name(def_id);
-                Some(tcx.mk_const(ty::ConstKind::Param(ty::ParamConst::new(index, name)), ty))
+                Some(tcx.mk_const(ty::ParamConst::new(index, name), ty))
             }
             _ => None,
         }
@@ -143,7 +143,7 @@ impl<'tcx> Const<'tcx> {
     /// Interns the given value as a constant.
     #[inline]
     pub fn from_value(tcx: TyCtxt<'tcx>, val: ty::ValTree<'tcx>, ty: Ty<'tcx>) -> Self {
-        tcx.mk_const(ConstKind::Value(val), ty)
+        tcx.mk_const(val, ty)
     }
 
     /// Panics if self.kind != ty::ConstKind::Value

compiler/rustc_middle/src/ty/relate.rs

@@ -663,10 +663,7 @@ pub fn super_relate_consts<'tcx, R: TypeRelation<'tcx>>(
                 au.substs,
                 bu.substs,
             )?;
-            return Ok(tcx.mk_const(
-                ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def: au.def, substs }),
-                a.ty(),
-            ));
+            return Ok(tcx.mk_const(ty::UnevaluatedConst { def: au.def, substs }, a.ty()));
         }
         // Before calling relate on exprs, it is necessary to ensure that the nested consts
         // have identical types.