RFR(XS): 8030184 Remove unneeded "content_type" declarations from tracetypes.xml

[Staffan Larsen]

tracetypes.xml has declarations of a couple of content_types that are never 
used.

bug: https://bugs.openjdk.java.net/browse/JDK-8030184
webrev: http://cr.openjdk.java.net/~sla/8030184/webrev.00/

Thanks,
/Staffan