[GTK] Unreviewed test gardening

[GTK] Unreviewed test gardening
https://bugs.webkit.org/show_bug.cgi?id=169534

Unreviewed GTK+ gardening.

Rebaseline tests:
LayoutTests/imported/w3c:

   - imported/w3c/web-platform-tests/XMLHttpRequest/getresponseheader-case-insensitive.html

* web-platform-tests/XMLHttpRequest/getresponseheader-case-insensitive-expected.txt:

LayoutTests:

   - http/tests/xmlhttprequest/xmlhttprequest-test-custom-headers.html

* platform/gtk/TestExpectations:
   - fast/text/font-selection-font-face-parse.html [ Skip ]
* platform/gtk/http/tests/xmlhttprequest/xmlhttprequest-test-custom-headers-expected.txt:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@213775 268f45cc-cd09-0410-ab3c-d52691b4dbfc