cleanup whitespace

parallel_hashmap/phmap.h

@@ -3450,8 +3450,6 @@ public:
         return true;
     }
 
-    
-
     template <class K = key_type, class P = Policy, K* = nullptr>
     MappedReference<P> operator[](key_arg<K>&& key) {
         return Policy::value(&*try_emplace(std::forward<K>(key)).first);