doc: fix explanation of package.json "type" field
Remove erroneous reference to files with .mjs
extension, which are not affected by the "type" field.
Checklist
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documentation is changed or added -
commit message follows commit guidelines
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Remove erroneous reference to files with .mjs
extension, which are not affected by the "type" field.