Kernel/Devices: Remove required_mode and device_name methods

These methods are no longer needed because SystemServer is able to
populate the DevFS on its own.

Device absolute_path no longer assume a path to the /dev location,
because it really should not assume any path to a Device node.

Because StorageManagement still needs to know the storage name, we
declare a virtual method only for StorageDevices to override, but this
technique should really be removed later on.

Kernel/TTY/TTY.h

@@ -49,9 +49,6 @@ public:
     void set_default_termios();
     void hang_up();
 
-    // ^Device
-    virtual mode_t required_mode() const override { return 0620; }
-
 protected:
     virtual KResultOr<size_t> on_tty_write(const UserOrKernelBuffer&, size_t) = 0;
     void set_size(unsigned short columns, unsigned short rows);