update sqlserver custom metrics guidance

[EmmaOnThursday]

What does this PR do?

Updates to SQL server documentation:

• Remove a section on using stored procedures to collect custom metrics, which is no longer recommended
• A few small cleanups in .yaml examples and elsewhere

Motivation

Additional Notes

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Reviewer checklist

• [ ] Review the changed files.
• [ ] Review the URLs listed in the Preview section.
• [ ] Check images for PII
• [ ] Review any mentions of "Contact Datadog support" for internal support documentation.

[github-actions[bot]]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/emma/sql-server-custom-metrics/integrations/guide/collect-sql-server-custom-metrics