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/Tests/TestHashMap.cpp

@@ -31,7 +31,7 @@
 
 TEST_CASE(construct)
 {
-    typedef HashMap<int, int> IntIntMap;
+    using IntIntMap = HashMap<int, int>;
     EXPECT(IntIntMap().is_empty());
     EXPECT_EQ(IntIntMap().size(), 0u);
 }