The file only contains obsolete definitions, so it really belongs in
`lisp/obsolete`. Moving it there will also signal a warning for those
people who run old `.elc` files using EIEIO and generated with
Emacs<25 and who otherwise might not know about the obsolescence of
some of the functions they use.
* lisp/emacs-lisp/eieio-compat.el: Move to ...
* lisp/obsolete/eieio-compat.el: ... here.