chore: reuse proxyutil import for proxy

[a7i]

What type of PR is this?

/kind cleanup

What this PR does / why we need it: remove extra import and reuse proxyutil

Which issue(s) this PR fixes: N/A

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 53.12%. Comparing base (167f213) to head (2f3ac7d).

Files	Patch %	Lines
pkg/util/proxy/proxy.go	0.00%	2 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #4906 +/- ## ========================================== - Coverage 53.13% 53.12% -0.01% ========================================== Files 251 251 Lines 20415 20415 ========================================== - Hits 10848 10846 -2 - Misses 8853 8855 +2 Partials 714 714 ``` | [Flag](https://app.codecov.io/gh/karmada-io/karmada/pull/4906/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=karmada-io) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/karmada-io/karmada/pull/4906/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=karmada-io) | `53.12% <0.00%> (-0.01%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=karmada-io#carryforward-flags-in-the-pull-request-comment) to find out more.

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[zhzhuang-zju]

/lgtm

[RainbowMango]

/lgtm /assign @chaunceyjiang

[liangyuanpeng]

/lgtm

[RainbowMango]

/assign @whitewindmills as well

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chaunceyjiang

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