QPID-4514: Remove IO readCredit throttling only used by removed cluster code

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1440616 13f79535-47bb-0310-9956-ffa450edef68
QPID-4514: Remove IO start/stop reading primitives used by removed cluster

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1440617 13f79535-47bb-0310-9956-ffa450edef68