revert prometheus service monitor selector

[junotx]

It just synchronizes update in https://github.com/kubesphere/ks-prometheus/pull/5 to here.

/cc @benjaminhuo

[benjaminhuo]

/lgtm

[ks-ci-bot]

LGTM label has been added.

Git tree hash: d97ba2f26ebc50957b015fd727d3bbe748f52771

[benjaminhuo]

/approve

[ks-ci-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[pixiake]

/cherrypick release-3.3

[ks-ci-bot]

@pixiake: new pull request created: #1958

In response to this:

/cherrypick release-3.3

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