yuzu/bootmanager: Default EmuThread's destructor in the cpp file

This class contains non-trivial members, so we should default the
destructor's definition within the cpp file.

src/yuzu/bootmanager.cpp

@@ -26,6 +26,8 @@
 
 EmuThread::EmuThread(GRenderWindow* render_window) : render_window(render_window) {}
 
+EmuThread::~EmuThread() = default;
+
 void EmuThread::run() {
     render_window->MakeCurrent();