The reason why you are seeing the error is because RestEasy has a dependency on httpclient jars which is provided as a jboss module. The version you provided is conflicting with the one provided by JBoss .
Why do you need to package the HTTPClient jars with your web app? Is it for some rest client call? In that case you should use RestEasy which is the default JAX-RS implementation on JBoss AS7. It will be a better framework to use for that purpose.
Your other option is to add a dependency on the org.apache.httpcomponents
module in your WEB-INF\jboss-deployment-structure.xml
and remove the http-client jars from WEB-INF\lib
.