Unrolled build for #142747

Rollup merge of #142747 - nnethercote:json-conversion-cleanups, r=aDotInTheVoid

rustdoc_json: conversion cleanups

A bunch of clean-to-types conversion cleanups I found while working on perf-related stuff in rustdoc_json.

r? ```@aDotInTheVoid```

Author: rust-timer

src/librustdoc/clean/types.rs

@@ -2432,20 +2432,6 @@ pub(crate) enum ConstantKind {
     Infer,
 }
 
-impl Constant {
-    pub(crate) fn expr(&self, tcx: TyCtxt<'_>) -> String {
-        self.kind.expr(tcx)
-    }
-
-    pub(crate) fn value(&self, tcx: TyCtxt<'_>) -> Option<String> {
-        self.kind.value(tcx)
-    }
-
-    pub(crate) fn is_literal(&self, tcx: TyCtxt<'_>) -> bool {
-        self.kind.is_literal(tcx)
-    }
-}
-
 impl ConstantKind {
     pub(crate) fn expr(&self, tcx: TyCtxt<'_>) -> String {
         match *self {