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/KCOVDevice.cpp

@@ -141,9 +141,4 @@ KResultOr<Memory::Region*> KCOVDevice::mmap(Process& process, OpenFileDescriptio
         range, *kcov_instance->vmobject(), offset, {}, prot, shared);
 }
 
-String KCOVDevice::device_name() const
-{
-    return "kcov"sv;
-}
-
 }