AK: Prefer using instead of typedef

Problem:
- `typedef` is a keyword which comes from C and carries with it old
  syntax that is hard to read.
- Creating type aliases with the `using` keyword allows for easier
  future maintenance because it supports template syntax.
- There is inconsistent use of `typedef` vs `using`.

Solution:
- Use `clang-tidy`'s checker called `modernize-use-using` to update
  the syntax to use the newer syntax.
- Remove unused functions to make `clang-tidy` happy.
- This results in consistency within the codebase.

AK/HashMap.h

@@ -67,9 +67,9 @@ public:
     }
     void remove_one_randomly() { m_table.remove(m_table.begin()); }
 
-    typedef HashTable<Entry, EntryTraits> HashTableType;
-    typedef typename HashTableType::Iterator IteratorType;
-    typedef typename HashTableType::ConstIterator ConstIteratorType;
+    using HashTableType = HashTable<Entry, EntryTraits>;
+    using IteratorType = typename HashTableType::Iterator;
+    using ConstIteratorType = typename HashTableType::ConstIterator;
 
     IteratorType begin() { return m_table.begin(); }
     IteratorType end() { return m_table.end(); }