PLT-6543 Fixed markdown images from overflowing width of post list (#6584)

webapp/sass/layout/_markdown.scss

@@ -52,7 +52,6 @@ h6 {
         -moz-force-broken-image-icon: 1;
         margin: 5px 0;
         max-height: 500px;
-        max-width: 500px;
     }
 }
 
@@ -214,4 +213,4 @@ code {
         font-size: 1.2em;
         margin-top: 30px;
     }
-}
+}