configure_hotkeys: Move conflict detection logic to IsUsedKey()

We don't need to extract the entire set of hotkeys into a list and then
iterate through it. We can traverse the list and early-exit if we're
able to.

src/yuzu/configuration/configure_hotkeys.h

@@ -34,7 +34,6 @@ public:
 private:
     void Configure(QModelIndex index);
     bool IsUsedKey(QKeySequence key_sequence) const;
-    QList<QKeySequence> GetUsedKeyList() const;
 
     std::unique_ptr<Ui::ConfigureHotkeys> ui;