cleanup code for ZkBookieRackAffinityMapping

[StevenLuMT]

Descriptions of the changes in this PR:

Motivation

Simple code cleanup

Modifications

1. no use import UnknownHostException for ZkBookieRackAffinityMapping

[github-actions]

@StevenLuMT:Thanks for your contribution. For this PR, do we need to update docs?
(The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)

[nicoloboschi]

I see checkstyle shows 63 errors for pulsar-zookkeeper-utils, including unused imports. (the one @StevenLuMT is fixing in this PR)
Is there any reason why we don't strictly follow checkstyle and attach it at the compile phase in every sub-projects? @eolivelli @lhotari @codelipenghui @merlimat

[hezhangjian]

The master doesn't have this problem at now.

[hezhangjian]

I see checkstyle shows 63 errors for pulsar-zookkeeper-utils, including unused imports. (the one @StevenLuMT is fixing in this PR) Is there any reason why we don't strictly follow checkstyle and attach it at the compile phase in every sub-projects? @eolivelli @lhotari @codelipenghui @merlimat
In my memory, this config of checkstyle only checks file that modified not every file in the project

[codelipenghui]

@nicoloboschi I think we have some component have not apply the check style yet.

[codelipenghui]

@StevenLuMT could you please help resolve the conflicts?

[merlimat]

This class was already deleted/refactored in master branch

[Anonymitaet]

@StevenLuMT for the doc side, this PR cleanup codes, so no need to update docs, correct?

[codelipenghui]

This class was already deleted/refactored in master branch

Sorry @StevenLuMT I will close the PR for now