BAN: Rewrite HashMap as a wrapper around HashSet

There is really no need to have two implementation of the same thing.
Only difference now is that HashMap's value type has to be movable but
this wasn't an issue

userspace/programs/resolver/main.cpp

@@ -3,6 +3,7 @@
 #include <BAN/Endianness.h>
 #include <BAN/HashMap.h>
 #include <BAN/IPv4.h>
+#include <BAN/LinkedList.h>
 #include <BAN/String.h>
 #include <BAN/StringView.h>
 #include <BAN/Vector.h>