[CMAKE] WebProcess shouldn't need to explicitly link to JavaScriptCore and WebCore
https://bugs.webkit.org/show_bug.cgi?id=135832

Reviewed by Gyuyoung Kim.

Linking to WebKit2 should be enough, like Network and Plugin processes.

* CMakeLists.txt:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@172516 268f45cc-cd09-0410-ab3c-d52691b4dbfc