ISPN-2740 NPE at AbstractEnlistmentAdapter

The NPE was caused by null rpcManager in local mode during execution of removeTransactionInfoRemotely(). Actually, removeTransactionInfoRemotely() should only execute if the cache is clustered. The already existing isClustered() check was using logic short-circuiting and was miss-placed, so I moved it outside the method.

JIRA: https://issues.jboss.org/browse/ISPN-2740