DevTools: 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/DevTools/Profiler/TimelineHeader.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022, the SerenityOS developers.
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -27,10 +28,6 @@ TimelineHeader::TimelineHeader(Profile& profile, Process const& process)
     m_text = String::formatted("{} ({})", LexicalPath::basename(m_process.executable), m_process.pid);
 }
 
-TimelineHeader::~TimelineHeader()
-{
-}
-
 void TimelineHeader::paint_event(GUI::PaintEvent& event)
 {
     GUI::Frame::paint_event(event);