[GTK] Disable Shadow DOM feature
https://bugs.webkit.org/show_bug.cgi?id=115374

Reviewed by Martin Robinson.

Disable the Shadow DOM feature on the GTK port, the feature is planned for removal.

.: 

* Source/autotools/SetupWebKitFeatures.m4:

Tools: 

* Scripts/webkitperl/FeatureList.pm:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149352 268f45cc-cd09-0410-ab3c-d52691b4dbfc