Kernel: Remove use of copy_ref() in favor of regular RefPtr copies.

This is obviously more readable. If we ever run into a situation where
ref count churn is actually causing trouble in the future, we can deal with
it then. For now, let's keep it simple. :^)

Kernel/FileSystem/Ext2FileSystem.h

@@ -60,7 +60,7 @@ class Ext2FS final : public DiskBackedFS {
     friend class Ext2FSInode;
 
 public:
-    static NonnullRefPtr<Ext2FS> create(NonnullRefPtr<DiskDevice>&&);
+    static NonnullRefPtr<Ext2FS> create(NonnullRefPtr<DiskDevice>);
     virtual ~Ext2FS() override;
     virtual bool initialize() override;