[Qt] DRT sideeffect revealed by r63657
https://bugs.webkit.org/show_bug.cgi?id=42578

Remove incorrect Qt specific expected file for http/tests/security/mixedContent/insecure-css-in-main-frame.html.
Platform independent is the correct one.

Add http/tests/security/mixedContent/insecure-css-in-main-frame.html 
to the Skipped list, because it is a flakey test due to this bug.

* platform/qt/Skipped:
* platform/qt/http/tests/security/mixedContent/insecure-css-in-main-frame-expected.txt: Removed.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@70498 268f45cc-cd09-0410-ab3c-d52691b4dbfc