[WK2] Remove more obsolete shim code
        https://bugs.webkit.org/show_bug.cgi?id=106248

        Reviewed by Anders Carlsson.

        Removing KeychainItemShimCallbacks, and SecItemRequestData::CopyContent, which was
        only needed for that obsolete version of shim.

        We now use WebProcessSecItemShimCallbacks.

        * Shared/mac/SecItemRequestData.h:
        * UIProcess/mac/WebProcessProxyMac.mm:
        (WebKit::handleSecItemRequest):
        * WebProcess/mac/WebProcessShim.h:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@138982 268f45cc-cd09-0410-ab3c-d52691b4dbfc