[Cocoa] WKUIDelegate.h is a project header
https://bugs.webkit.org/show_bug.cgi?id=129215

Reviewed by Anders Carlsson.

* WebKit2.xcodeproj/project.pbxproj: Make it a public header.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@164550 268f45cc-cd09-0410-ab3c-d52691b4dbfc