[SPARK-3305] Remove unused import from UI classes.

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #2200 from sarutak/SPARK-3305 and squashes the following commits:

3cbd6ee [Kousuke Saruta] Removed unused import from classes related to UI
[SPARK-2288] Hide ShuffleBlockManager behind ShuffleManager

By Hiding the shuffleblockmanager behind Shufflemanager, we decouple the shuffle data's block mapping management work from Diskblockmananger. This give a more clear interface and more easy for other shuffle manager to implement their own block management logic. the jira ticket have more details.

Author: Raymond Liu <raymond.liu@intel.com>

Closes #1241 from colorant/shuffle and squashes the following commits:

0e01ae3 [Raymond Liu] Move ShuffleBlockmanager behind shuffleManager
Manually close old pull requests
Closes #1824