Remove platform specific expectations for http/tests/xmlhttprequest/origin-exact-matching tests

We have some platform specific expectations for some of
http/tests/xmlhttprequest/origin-exact-matching layout tests
for mountainlion.

They're identical to general expectations.

R=sigbjornf
BUG=344294

Review URL: https://codereview.chromium.org/641603005

git-svn-id: svn://svn.chromium.org/blink/trunk@184649 bbb929c8-8fbe-4397-9dbb-9b2b20218538