Rocky mistake with key frame in timeline it looks like that i made a mistake with the timeline. I have deleted objects from the file, left the one that i wish to work on, which i did (worked) and even saved the file. Today I have opened the file and wanted to add some keyframes to my rigs but, sadly, by removing the old objects and forgetting to remove their keyframes, now i came accrose to be unable to remove the left over keyframes from the old objecs and my file is irrecoverable (ctrl+Z will not work any more since file was edited and saved, closed and then opened). I might even say that i have "ghost" keyframes in my timeline that I just can't remove them in any way. I have searched on youtube, on google, in the book but nothing was mentioned (or i haven't paid attention well) for removing this "ghosts".
I have only the lines in the timeline, nothing else nowhere (nothing in dope sheet, NLA editor, graph editor, just in timeline).

If someone could advice me how to remove them, I would be a very happy man. 

Thank you in advance.

The file of the issue at hand:
You got this object 'GPencil' in your Outliner. It's not selectable, but could be made invisible. This is the object which has the keyframes. Strangely, it can't be deleted, since it's not selectable. But you could just create an empty new blender file, and append all objects from your old scene into the new one - the broken object is not among them.