Refactor python files of suggestion services

[c-bata]

What this PR does / why we need it:

• Remove unused imports.
• Remove redundant parentheses.
• Use new-style classes because suggestion modules are run on Python 3.6 (See Dockerfiles in cmd/suggestion.
• Follow pep8.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
None.

Special notes for your reviewer:
None

Release note:

NONE

[kubeflow-bot]

This change is 

[k8s-ci-robot]

Hi @c-bata. Thanks for your PR.

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[c-bata]

/assign @gaocegege

[gaocegege]

/lgtm
/approve

Thanks for your contribution! 🎉 👍

/ok-to-test

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gaocegege

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