[GTK] Cleanup TestExpectations to pass --lint-test-files
https://bugs.webkit.org/show_bug.cgi?id=116419

Unreviewed GTK gardening.

Remove one of two http/tests/cache/willsendrequest-returns-null-for-memory-cache-load.html

Patch by Seokju Kwon <seokju.kwon@gmail.com> on 2013-05-20

* platform/gtk/TestExpectations:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150374 268f45cc-cd09-0410-ab3c-d52691b4dbfc