Remove TraitAlias from trait_of_item

This is dead code.

Author: camsteffen

compiler/rustc_middle/src/ty/mod.rs

@@ -1994,7 +1994,7 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn trait_of_item(self, def_id: DefId) -> Option<DefId> {
         if let DefKind::AssocConst | DefKind::AssocFn | DefKind::AssocTy = self.def_kind(def_id) {
             let parent = self.parent(def_id);
-            if let DefKind::Trait | DefKind::TraitAlias = self.def_kind(parent) {
+            if let DefKind::Trait = self.def_kind(parent) {
                 return Some(parent);
             }
         }