qt: Default destructors where applicable

Makes code consistent with our style of defaulting special member
functions where applicable.

src/yuzu/debugger/wait_tree.cpp

@@ -14,7 +14,7 @@
 #include "core/hle/kernel/timer.h"
 #include "core/hle/kernel/wait_object.h"
 
-WaitTreeItem::~WaitTreeItem() {}
+WaitTreeItem::~WaitTreeItem() = default;
 
 QColor WaitTreeItem::GetColor() const {
     return QColor(Qt::GlobalColor::black);