yuzu/configuration: Make slots private where applicable

These slots are only ever attached to event handling mechanisms within
the class itself, they're never used externally. Because of this, we can
make the functions private.

This also removes redundant usages of the private access specifier.

src/yuzu/configuration/configure_debug.h

@@ -23,6 +23,5 @@ public:
 private:
     void setConfiguration();
 
-private:
     std::unique_ptr<Ui::ConfigureDebug> ui;
 };