Applications: Use default constructors/destructors

https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#cother-other-default-operation-rules

"The compiler is more likely to get the default semantics right and
you cannot implement these functions better than the compiler."

Userland/Applications/SpaceAnalyzer/TreeMapWidget.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, the SerenityOS developers.
+ * Copyright (c) 2021-2022, the SerenityOS developers.
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -15,15 +15,6 @@ REGISTER_WIDGET(SpaceAnalyzer, TreeMapWidget)
 
 namespace SpaceAnalyzer {
 
-TreeMapWidget::TreeMapWidget()
-    : m_viewpoint(0)
-{
-}
-
-TreeMapWidget::~TreeMapWidget()
-{
-}
-
 static const Color colors[] = {
     Color(253, 231, 37),
     Color(148, 216, 64),