CppEditor: Do not add QuickFixFactories to object pool anymore

Not needed anymore.

Also some cleanup, no 'using' in headers etc.

Change-Id: I8c4547d80d0c0ffd989d1efbc74687c9f56096a4
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/cppeditor/cppquickfix_test.cpp

@@ -48,6 +48,7 @@
 using namespace Core;
 using namespace CPlusPlus;
 using namespace CppEditor::Internal::Tests;
+using namespace CppTools;
 using namespace TextEditor;
 
 using CppTools::Tests::TestIncludePaths;