Remove Resolver::empty_disambiguator.

It was added in rust-lang#115367 for anonymous ADTs. Those changes were then
reverted in rust-lang#131045, but `empty_disambiguator` was left behind, perhaps
by mistake. It seems to be unnecessary.

Author: nnethercote

compiler/rustc_resolve/src/lib.rs

@@ -1082,8 +1082,6 @@ pub struct Resolver<'ra, 'tcx> {
     binding_parent_modules: FxHashMap<NameBinding<'ra>, Module<'ra>>,
 
     underscore_disambiguator: u32,
-    /// Disambiguator for anonymous adts.
-    empty_disambiguator: u32,
 
     /// Maps glob imports to the names of items actually imported.
     glob_map: FxHashMap<LocalDefId, FxHashSet<Symbol>>,
@@ -1462,7 +1460,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             module_children: Default::default(),
             trait_map: NodeMap::default(),
             underscore_disambiguator: 0,
-            empty_disambiguator: 0,
             empty_module,
             module_map,
             block_map: Default::default(),
@@ -1841,9 +1838,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         let disambiguator = if ident.name == kw::Underscore {
             self.underscore_disambiguator += 1;
             self.underscore_disambiguator
-        } else if ident.name == kw::Empty {
-            self.empty_disambiguator += 1;
-            self.empty_disambiguator
         } else {
             0
         };