Remove unused opt_local_def_id_to_hir_id function

Found while investigating rust-lang#82933 - all LocalDefIds are expected to have
HirIds, there's no point in pretending otherwise.

Author: jyn514

compiler/rustc_hir/src/definitions.rs

@@ -342,11 +342,6 @@ impl Definitions {
         self.def_id_to_hir_id[id].unwrap()
     }
 
-    #[inline]
-    pub fn opt_local_def_id_to_hir_id(&self, id: LocalDefId) -> Option<hir::HirId> {
-        self.def_id_to_hir_id[id]
-    }
-
     #[inline]
     pub fn opt_hir_id_to_local_def_id(&self, hir_id: hir::HirId) -> Option<LocalDefId> {
         self.hir_id_to_def_id.get(&hir_id).copied()

compiler/rustc_middle/src/hir/map/mod.rs

@@ -180,11 +180,6 @@ impl<'hir> Map<'hir> {
         self.tcx.definitions.local_def_id_to_hir_id(def_id)
     }
 
-    #[inline]
-    pub fn opt_local_def_id_to_hir_id(&self, def_id: LocalDefId) -> Option<HirId> {
-        self.tcx.definitions.opt_local_def_id_to_hir_id(def_id)
-    }
-
     pub fn iter_local_def_id(&self) -> impl Iterator<Item = LocalDefId> + '_ {
         self.tcx.definitions.iter_local_def_id()
     }