OioSctpChannel iterating over selected keys

Motivation:
OioSctpChannel.doReadMessages is iterating over the selected keys, and ignoring each selected key. It is not known why this is needed and no other channel implementation does this.

Modifications:
- Stop iterating over selected keys, and just read like other channels

Result:
No unnecessary iteration in OioSctpChannel.doReadMessages.
Fixes https://github.com/netty/netty/issues/3884

transport-sctp/src/main/java/io/netty/channel/sctp/oio/OioSctpChannel.java

@@ -184,9 +184,6 @@ public class OioSctpChannel extends AbstractOioMessageChannel
             return readMessages;
         }
 
-        Set<SelectionKey> reableKeys = readSelector.selectedKeys();
-        try {
-            for (SelectionKey ignored : reableKeys) {
         RecvByteBufAllocator.Handle allocHandle = this.allocHandle;
         if (allocHandle == null) {
             this.allocHandle = allocHandle = config().getRecvByteBufAllocator().newHandle();
@@ -214,10 +211,6 @@ public class OioSctpChannel extends AbstractOioMessageChannel
                 buffer.release();
             }
         }
-            }
-        } finally {
-            reableKeys.clear();
-        }
         return readMessages;
     }