[GTK] Re-enable gtk-doc in EWS
https://bugs.webkit.org/show_bug.cgi?id=128369

Reviewed by Carlos Garcia Campos.

Enable again gtk-doc generation in EWS once bug #128417 has been fixed.

* Scripts/webkitpy/common/config/ports.py:
(GtkPort.build_webkit_command): Add --disable-gtk-doc arg.
(GtkWK2Port.build_webkit_command): Ditto.
* Scripts/webkitpy/common/config/ports_unittest.py:
(DeprecatedPortTest.test_gtk_port): Ditto.
(DeprecatedPortTest.test_gtk_wk2_port): Ditto.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@164713 268f45cc-cd09-0410-ab3c-d52691b4dbfc