resolves #366 stop changing visited link color

We no longer change normal link color (since 3697bd9),
so for consistency (and fixing of night mode on iBooks) also do not touch visited links.

If we ever decide again to colorize links, this will need to be handled somehow differently

closes #367
followups 338

data/styles/epub3.css

@@ -242,12 +242,6 @@ body:first-of-type a:link {
   background-position: 0 1.2em;
 }
 
-body a:visited {
-  color: #333332;
-  /* hack for font color in iBooks */
-  -webkit-text-fill-color: #333332;
-}
-
 code.literal {
   /* don't let it affect line spacing */
   /* disable since M+ 1mn won't interrupt line height */
@@ -684,12 +678,6 @@ div.abstract > p {
   line-height: 1.75;
 }
 
-div.abstract > p a:link {
-  color: #333332;
-  /* hack for font color in iBooks */
-  -webkit-text-fill-color: #333332;
-}
-
 div.abstract > p:first-child::first-line {
   font-weight: bold;
   -webkit-font-feature-settings: "kern" off;