Wiki saved as EPUB: stylesheet fix (#3894)

Removed width:80% as it was never supported by crengine (the effect
was achieved thanks to margins and paddings).
Wikipedia saved articles from now on won't be effected by a double
effect if we later add full support for width: into crengine.

frontend/ui/wikipedia.lua

@@ -940,7 +940,6 @@ a.newwikinonexistent {
 }
 /* show a box around image thumbnails */
 div.thumb {
-    width: 80%;
     border: dotted 1px black;
     margin-top: 0.5em;
     margin-bottom: 0.5em;