Remove LangItems::require

It's just a short wrapper used by `tcx.require_lang_item`. Deleting it
gives us a negative diff.

compiler/rustc_hir/src/errors.rs

@@ -1,10 +0,0 @@
-use crate::LangItem;
-
-#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, Encodable, Decodable)]
-pub struct LangItemError(pub LangItem);
-
-impl ToString for LangItemError {
-    fn to_string(&self) -> String {
-        format!("requires `{}` lang_item", self.0.name())
-    }
-}

compiler/rustc_hir/src/lang_items.rs

@@ -8,7 +8,6 @@
 //! * Functions called by the compiler itself.
 
 use crate::def_id::DefId;
-use crate::errors::LangItemError;
 use crate::{MethodKind, Target};
 
 use rustc_ast as ast;
@@ -42,13 +41,6 @@ impl LanguageItems {
         self.items[item as usize] = Some(def_id);
     }
 
-    /// Requires that a given `LangItem` was bound and returns the corresponding `DefId`.
-    /// If it wasn't bound, e.g. due to a missing `#[lang = "<it.name()>"]`,
-    /// returns an error encapsulating the `LangItem`.
-    pub fn require(&self, it: LangItem) -> Result<DefId, LangItemError> {
-        self.get(it).ok_or_else(|| LangItemError(it))
-    }
-
     pub fn iter(&self) -> impl Iterator<Item = (LangItem, DefId)> + '_ {
         self.items
             .iter()

compiler/rustc_hir/src/lib.rs

@@ -30,7 +30,6 @@ pub mod def;
 pub mod def_path_hash_map;
 pub mod definitions;
 pub mod diagnostic_items;
-pub mod errors;
 pub use rustc_span::def_id;
 mod hir;
 pub mod hir_id;