(maint) Clean up gitignore

[hestonhoffman]

What does this PR do? What is the motivation?

• Removes some orphaned translated files where the English source has been replaced with mdoc files.
• Removes some accidentally committed cdoc files
• Updates the pre-commit hook to check for both orphaned files and incorrectly tracked files
• Updates content/.gitignore to remove duplicates.

Merge instructions

Merge readiness:

• Hold off on merge until the upstream PR is merged.

[datadog-datadog-prod-us1]

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