FIX[MQB]: cancelRead might cause a deadlock (#948)

Signed-off-by: Emelia Lei <wlei29@bloomberg.net>

Author: emelialei88

src/groups/mqb/mqba/mqba_adminsession.cpp

@@ -387,9 +387,6 @@ void AdminSession::tearDown(BSLA_UNUSED const bsl::shared_ptr<void>& session,
 {
     // executed by the *IO* thread
 
-    // Cancel the reads on the channel
-    d_channel_sp->cancelRead();
-
     // Enqueue an event to the client dispatcher thread and wait for it to
     // finish; only after this will we have the guarantee that no method will
     // try to use the channel.

src/groups/mqb/mqba/mqba_clientsession.cpp

@@ -2924,9 +2924,6 @@ void ClientSession::tearDown(const bsl::shared_ptr<void>& session,
 
     BALL_LOG_INFO << description() << ": tearDown";
 
-    // Cancel the reads on the channel
-    d_channel_sp->cancelRead();
-
     // Enqueue an event to the client dispatcher thread and wait for it to
     // finish; only after this will we have the guarantee that no method will
     // try to use the channel.