Revert "Replace MyEventReceiver KeyList with std::unordered_set" (#10622)

This reverts commit 787561b29a.

src/client/keycode.h

@@ -24,20 +24,12 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include <IEventReceiver.h>
 #include <string>
 
-class KeyPress;
-namespace std
-{
-	template <> struct hash<KeyPress>;
-}
-
 /* A key press, consisting of either an Irrlicht keycode
    or an actual char */
 
 class KeyPress
 {
 public:
-	friend struct std::hash<KeyPress>;
-
 	KeyPress() = default;
 
 	KeyPress(const char *name);
@@ -63,17 +55,6 @@ protected:
 	std::string m_name = "";
 };
 
-namespace std
-{
-	template <> struct hash<KeyPress>
-	{
-		size_t operator()(const KeyPress &key) const
-		{
-			return key.Key;
-		}
-	};
-}
-
 extern const KeyPress EscapeKey;
 extern const KeyPress CancelKey;