often those objects appear when you copy and paste data from a website or something like that.

to avoid them paste copied information as values then objects are not pasted.

to remove all the objects.

1. Press F5 key
2. Press Special button (bottom left)
3. Select last radiobutton called "objects"
4. Press OK button
5. Press Delete key

All objects should be gone now.

please be aware that also "normal'pictures of graphs are objects so they might be deleted too.
So you may want to test the actions on a copy of the file to see only stuff you do not need is deleted.