Fix obsolete variable warnings about class names

Fix obsolete variable warnings about class names

* lisp/emacs-lisp/eieio-core.el (eieio-defclass-autoload): Try to make
the wording of the warning about the obsoleted variable less confusing.
* lisp/emacs-lisp/bytecomp.el (byte-compile-check-variable): Don't
warn for lexical variables (Bug#39169).  Fix spurious `or'.
* test/lisp/emacs-lisp/bytecomp-tests.el
(bytecomp/warn-obsolete-variable-bound\.el): New test.
* test/lisp/emacs-lisp/bytecomp-resources/warn-obsolete-variable-bound.el:
New file.