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/Devices/SerialDevice.h

@@ -102,10 +102,6 @@ public:
         DataReady = 0x01 << 0
     };
 
-    // ^Device
-    virtual mode_t required_mode() const override { return 0620; }
-    virtual String device_name() const override;
-
 private:
     friend class PCISerialDevice;