bug#22605: 25.0.50; eww-readable hides images

[Artur Malabarba]

To reproduce:
1. M-x eww RET 
http://endlessparentheses.com/new-in-emacs-25-1-round-quotes-in-help-buffers.html
2. Type R

3. While the command correctly identifies the main part of the page, the
   two images that are part of the post's content (and were previously
   displayed correctly) will now be hidden. Their alt-text is displayed
   instead.

This might be intentional, as the docstring claims that it finds “the
main textual portion”. Still, images might be (and, in this case, are)
important for understanding the “main parts” of the page, so I would
like to suggest keeping them.