Get rid of two silly static null Strings
https://bugs.webkit.org/show_bug.cgi?id=111151

Reviewed by Eric Seidel.

We have a global null String through nullAtom, there is no need
for local static null strings.

* page/Page.cpp:
(WebCore::Page::groupName):
* rendering/RenderListItem.cpp:
(WebCore::RenderListItem::markerText):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144432 268f45cc-cd09-0410-ab3c-d52691b4dbfc