Cleanup/remove deprecate chains cmd

[adityavshinde]

Changes

fixes: #2751

• Removed pkg/cmd/chain/chain.go
• Removed pkg/cmd/chain/signature.go
• Removed pkg/cmd/chain/payload.go
• Removed docs/cmd/tkn_chain.md
• Removed docs/cmd/tkn_chain_signature.md
• Removed docs/cmd/tkn_chain_payload.md
• Modified pkg/cmd/root.go
• Modified pkg/cmd/testdata/TestPluginList.golden

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes tests (if functionality changed/added)
• Run the code checkers with make check
• Regenerate the manpages, docs and go formatting with make generated
• Commit messages follow commit message best practices

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Release Notes

[waveywaves]

@adityavshinde the CI isn't green here

[waveywaves]

cc @vdemeester

[anithapriyanatarajan]

/kind cleanup

[anithapriyanatarajan]

@pratap0007 @divyansh42 - could you help reviewing this PR. Thankyou

[divyansh42]

Thanks @adityavshinde for the PR!
Changes look good! Can you please squash the commits into two? We can keep one commit for the chains cmd removal and another one for the OCI buckets-related changes.

[adityavshinde]

Thanks @adityavshinde for the PR! Changes look good! Can you please squash the commits into two? We can keep one commit for the chains cmd removal and another one for the OCI buckets-related changes.

Thank you @divyansh42 for reviewing. I have squashed the commits into 2 commits.

[waveywaves]

Reviewing once before I put lgtm

[waveywaves]

/lgtm

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: divyansh42, waveywaves

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