lisp/*.el: More lexical-binding warnings' cleanups.
* tutorial.el (tutorial--describe-nonstandard-key): Use string-match-p.
(tutorial--detailed-help): Remove unused local variables.
(tutorial--save-tutorial-to): Use ignore-errors.
(help-with-tutorial): Use looking-at-p.
* view.el (view-buffer-other-window, view-buffer-other-frame):
Mark unused arguments.
* xml.el (xml-parse-tag-1, xml-parse-string): Use looking-at-p.
(xml-parse-dtd): Use looking-at-p, string-match-p. Mark unused
argument. Remove unused local variable.
(xml-parse-elem-type): Use string-match-p.
(xml-substitute-numeric-entities): Use ignore-errors.