Utils: More forward declarations / drop unused headers [H-K]

Round 1 - focus on headers.
For classes with initial in range [H-K].
Try to keep the same separators between different kind of headers.

Change-Id: Iefb032953743be41a847ee011c30527edfa425d8
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/autotest/autotestplugin.cpp

@@ -38,7 +38,6 @@
 #include "testsettingspage.h"
 #include "testtreeitem.h"
 #include "testtreemodel.h"
-#include "testtreeview.h"
 
 #include "boost/boosttestframework.h"
 #include "catch/catchframework.h"