Remove workaround for <rdar://problem/5321972>.
<rdar://problem/12022862> and https://bugs.webkit.org/show_bug.cgi?id=113516

Reviewed by Sam Weinig.

No new tests (No point in testing the removal of bizarre behavior).

* platform/network/mac/WebCoreURLResponse.mm:
(WebCore::adjustMIMETypeIfNecessary): This workaround isn't needed on Lion+

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147134 268f45cc-cd09-0410-ab3c-d52691b4dbfc