Kernel: Remove Inode's inheritance from Weakable

Nobody was using WeakPtr<Inode> anywhere, so there's no need for this
to inherit from Weakable.

Kernel/FileSystem/Inode.h

@@ -23,8 +23,7 @@
 
 namespace Kernel {
 
-class Inode : public RefCounted<Inode>
-    , public Weakable<Inode> {
+class Inode : public RefCounted<Inode> {
     friend class VirtualFileSystem;
     friend class FileSystem;