Disables Opera permutation

Opera uses webkit permutation with the recent Chromium based
versions and GWT will drop seperate Opera permutation in the
next release after 2.6.

Change-Id: Ifbde48ca3f41239cb3b19137b61c332cbddc334d
(cherry picked from commit 147ed73dd35de315379f0fc09920fef4a53d3606)

user/src/com/google/gwt/useragent/UserAgent.gwt.xml

diff --git a/user/src/com/google/gwt/useragent/UserAgent.gwt.xml b/user/src/com/google/gwt/useragent/UserAgent.gwt.xml
index c37aecc..6fcee79 100644
--- a/user/src/com/google/gwt/useragent/UserAgent.gwt.xml
+++ b/user/src/com/google/gwt/useragent/UserAgent.gwt.xml
@@ -24,7 +24,6 @@
   <define-property name="user.agent" values="ie8" />
   <extend-property name="user.agent" values="gecko1_8" />
   <extend-property name="user.agent" values="safari" />
-  <extend-property name="user.agent" values="opera" />
   <extend-property name="user.agent" values="ie9" fallback-value="ie8" />
   <extend-property name="user.agent" values="ie10" />
   <property-provider name="user.agent" generator="com.google.gwt.useragent.rebind.UserAgentPropertyGenerator"/>