Follow function aliases for `side-effect-free` and `pure` properties

Follow function aliases for `side-effect-free` and `pure` properties

This way we don't need to set these properties on aliases at all;
it was always easy to forget doing so.

* lisp/emacs-lisp/byte-opt.el (byte-opt--fget): New function.
(byte-optimize-form-code-walker, byte-optimize-form): Use it.
(side-effect-free-fns, side-effect-and-error-free-fns, pure-fns):
Remove aliases from lists, leaving only built-in functions.