Clean headers in CppTools.

Ran script to remove inludes on a trial-and-error basis and
manually corrected it.

Change-Id: Ic8464ea084ca1ab401e9f4a7d0183b92b4038902
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/completionsettingspage.cpp

@@ -35,10 +35,7 @@
 #include <coreplugin/icore.h>
 #include <texteditor/texteditorsettings.h>
 
-#include <extensionsystem/pluginmanager.h>
-
 #include <QTextStream>
-#include <QCoreApplication>
 
 using namespace CppTools;
 using namespace CppTools::Internal;