Core: Merge actionmanager/commandsfile pair into their only user

Also, de-QObject-ify and inline the Context wrapper structure
for the key strings.

Change-Id: I21f3afec61ef9ecfcc4c3d89afb9fb3a1548afae
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/actionmanager/commandmappings.cpp

@@ -18,8 +18,6 @@
 #include <QPushButton>
 #include <QTreeWidgetItem>
 
-Q_DECLARE_METATYPE(Core::Internal::ShortcutItem*)
-
 using namespace Utils;
 
 namespace Core {