* lisp/xwidget.el: Fix the interaction between `image-mode' and xwidget.
(xwidget-image-mode-navigation-adaptor
xwidget-image-mode-navigation-adaptor-p): `flet' has been deprecated and
`cl-flet' doesn't work like the old `flet', we now use a `defadvice'
around `image-display-size' instead.
(xwidget-webkit-mode-map): No need to use the adaptators now.