[SPARK-3281] Remove Netty specific code in BlockManager / shuffle

Netty functionality will be added back in subsequent PRs by using the BlockTransferService interface.

Author: Reynold Xin <rxin@apache.org>

Closes #2181 from rxin/SPARK-3281 and squashes the following commits:

5494b0e [Reynold Xin] Fix extra port.
ff6d1e1 [Reynold Xin] [SPARK-3281] Remove Netty specific code in BlockManager.