kernel: Replace usage of boost::intrusive_ptr with std::shared_ptr for kernel objects. (#3154)

* kernel: Replace usage of boost::intrusive_ptr with std::shared_ptr for kernel objects.

- See https://github.com/citra-emu/citra/pull/4710 for details.

src/core/hle/service/service.h

@@ -65,7 +65,7 @@ public:
     /// Creates a port pair and registers it on the kernel's global port registry.
     void InstallAsNamedPort();
     /// Creates and returns an unregistered port for the service.
-    Kernel::SharedPtr<Kernel::ClientPort> CreatePort();
+    std::shared_ptr<Kernel::ClientPort> CreatePort();
 
     void InvokeRequest(Kernel::HLERequestContext& ctx);