Don't enforce :protection in EIEIO objects any more

Don't enforce :protection in EIEIO objects any more

* doc/misc/eieio.texi (Slot Options): Document :protection as unsupported.

* lisp/emacs-lisp/eieio-core.el (eieio--scoped-class-stack): Remove var.
(eieio--scoped-class): Remove function.
(eieio--with-scoped-class): Remove macro.  Replace uses with `progn'.
(eieio--slot-name-index): Don't check the :protection anymore.
(eieio-initializing-object): Remove var.
(eieio-set-defaults): Don't let-bind eieio-initializing-object.

* lisp/emacs-lisp/eieio-generic.el (call-next-method): Don't bother checking
eieio--scoped-class any more.

* test/automated/eieio-test-methodinvoke.el (eieio-test-method-store):
Use an explicit arg instead of eieio--scoped-class.  Update all callers.

* test/automated/eieio-tests.el (eieio-test-25-slot-tests)
(eieio-test-26-default-inheritance, eieio-test-28-slot-protection)
(eieio-test-30-slot-attribute-override)
(eieio-test-31-slot-attribute-override-class-allocation): Don't check
that we enforce :protection since we don't any more.