style: Remove useless declarations in servo.css.

Margin is a reset property, there's no point in setting it to zero since it's
zero by default.

resources/servo.css

@@ -197,16 +197,10 @@ svg > * {
 
 /* style for text node. */
 *|*::-servo-text {
-    margin: 0;
     text-overflow: inherit;
     overflow: inherit;
 }
 
-/* style for text in input elements. */
-*|*::-servo-input-text {
-    margin: 0;
-}
-
 *|*::-servo-table-wrapper {
     display: table;
     border: none;