LayoutRegionMediaDelete calls Media->Delete to delete link

It must delete the link record using the LKID provided - the API method actually doesn't have enough information to do this for stored media - it needs the LKID to be provided.

hm ,I don't understand you comment:
you say "It must delete the link record using the LKID provided "
yes but this is already done in
region.data.class in function RemoveMedia(): it calls function RemoveDbLink() who sends an
"DELETE FROM lklayoutmedia WHERE lklayoutmediaID = $lkid ";
the lkid is taken from the XML - Node from Table "layout", that is removed from the "layout" xml just before.
therefore I don't understand why you say:
"the API method actually doesn't have enough information to do this for stored media-it needs the LKID to be provided " ?

On the other hand :
I used LayoutRegionLibraryAdd to add an existing media to a region.
but there is currently no "LayoutRegionLibraryDelete" in the API , just the "LayoutRegionMediaDelete", which I tried to use then.

So do we actually need a new API function called "LayoutRegionLibraryDelete" which is exactly the same as LayoutRegionMediaDelete with the exception of the line
"if (!$media->Delete($mediaId))
            return $this->Error($media->GetErrorNumber(), $media->GetErrorMessage());"
which would be omitted for LayoutRegionLibraryDelete() ?

The method is wrong - it is not good enough to have the media id because if the same media item is linked to a region timeline more than once - we will not know which one we are editing.

The API call must have the LKID provided.

It is also incorrect to delete the actual media file - that should be a separate call to LibraryDelete