Adjust some `pure` and `side-effect-free` function declarations

Adjust some `pure` and `side-effect-free` function declarations

* lisp/emacs-lisp/byte-opt.el (side-effect-free-fns):
Add `format-message` and `substring-no-properties`.
* lisp/subr.el (number-sequence, copy-tree, looking-at-p)
(string-match-p, string-trim-right, string-lines):
Declare side-effect-free.
(syntax-class, version-list-<, version-list-=, version-list-<=)
(version-list-not-zero): Declare pure and side-effect-free.
(ensure-list): Declare side-effect-free and error-free.
(string-equal-ignore-case): Remove `pure` declaration.
We may want it to be pure but right now it's not.