base: remove Cancelable_lock

- base/cancelable_lock.h becomes base/lock.h
- all members become private within base/lock.h
- solely Mutex and Blockade are friends to use base/lock.h

Fixes #3819

repos/base-sel4/src/core/include/rpc_cap_factory.h

@@ -15,7 +15,6 @@
 #define _CORE__INCLUDE__RPC_CAP_FACTORY_H_
 
 #include <base/allocator.h>
-#include <base/lock.h>
 #include <base/capability.h>
 
 namespace Genode { class Rpc_cap_factory; }