kern: delete KWritableEvent, devirtualize KReadableEvent Signal/Clear

libraries/libmesosphere/include/mesosphere/kern_k_client_session.hpp

@@ -20,6 +20,7 @@
 namespace ams::kern {
 
     class KSession;
+    class KEvent;
 
     class KClientSession final : public KAutoObject {
         MESOSPHERE_AUTOOBJECT_TRAITS(KClientSession, KAutoObject);
@@ -39,7 +40,7 @@ namespace ams::kern {
             constexpr KSession *GetParent() const { return m_parent; }
 
             Result SendSyncRequest(uintptr_t address, size_t size);
-            Result SendAsyncRequest(KWritableEvent *event, uintptr_t address, size_t size);
+            Result SendAsyncRequest(KEvent *event, uintptr_t address, size_t size);
 
             void OnServerClosed();
     };