Before running Overkill I see 4 objects looking like this:

After running Overkill I see 1 object looking like this:

You can also try this code and enter at the command prompt: REM
; rem function removes duplicates but keeps the one initially selected
; OP:
; https://forums.autodesk.com/t5/visual-lisp-autolisp-and-general/how-can-i-remove-same-object-of-repeat-by-lisp/m-p/13305272#M478451
(defun c:rem (/ ss)
(if (setq ss (ssget "_+.:E:S"))
(progn
(command "_.selectsimilar" ss "")
(if (ssget "_P")
(progn
(command "_.Erase" "_P" "_R" (ssname ss 0) "")
(sssetfirst nil ss)
)
)
)
)
(princ)
)
Afterwards you should see only 1 object looking like this:
