[Qualys VMDR] Fix duplicate fields in transform

[moxarth-rathod]

Proposed commit message

qualys_vmdr: remove duplicate fields in transform as per the comment [1] in this PR [2]. Also, remove 
unsupported field `source` from the fields definition. 
- [1] https://github.com/elastic/integrations/pull/16727#issuecomment-3719541508
- [2] https://github.com/elastic/integrations/pull/16727

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.
• I have verified that any added dashboard complies with Kibana's Dashboard good practices

Related issues

• Relates [qualys_vmdr]: Deprecation of API 2.0/3.0 for Knowledge Base #16640

[elasticmachine]

Pinging @elastic/security-service-integrations (Team:Security-Service Integrations)

[mrodm]

Just in case, this field was not reported as duplicated in https://buildkite.com/elastic/integrations/builds/36182#019b9848-4c98-49a8-8af1-fac140f6e491/L479

[moxarth-rathod]

This field is currently not supported. To avoid any potential confusion or unexpected behaviour, it would be good to remove it from the field definition.

[kcreddy]

Can you elaborate on why we are removing this field? It seems to be present even in the DTD of new API: #16640 (comment)
Any field removal even if unsupported by the API should be a breaking-change.

[elastic-vault-github-plugin-prod]

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[elasticmachine]

💚 Build Succeeded

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• Commit: 1bf9f7c

cc @moxarth-rathod