Remove an obsolete workaround for relaxing 3rd party cookie policy
https://bugs.webkit.org/show_bug.cgi?id=110664

Reviewed by Benjamin Poulain.

Removed shouldRelaxThirdPartyCookiePolicy(). This workaround is no longer needed,
because CFNetwork performs the same check starting with 10.6.8.

Also, the workaround was not quite correct and harmful for performance, as it
was always changing main document URL to an untrue value, which caused ResourceRequest
regeneration.

* platform/network/ResourceHandle.h:
* platform/network/cf/ResourceHandleCFNet.cpp:
(WebCore::ResourceHandle::createCFURLConnection):
(WebCore::ResourceHandle::start):
(WebCore::ResourceHandle::platformLoadResourceSynchronously):
* platform/network/mac/ResourceHandleMac.mm:
(WebCore::ResourceHandle::createNSURLConnection):
(WebCore::ResourceHandle::start):
(WebCore::ResourceHandle::platformLoadResourceSynchronously):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143939 268f45cc-cd09-0410-ab3c-d52691b4dbfc