Remove unnecessary Open-XML-SDK moniker

[twsouthwick]

The documentation is all about the SDK and all the extra places where
(Open-XML-SDK) is unnecessary.

[learn-build-service-prod]

Learn Build status updates of commit 4217bca:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/about-the-open-xml-sdk.md	✅Succeeded
docs/general/how-to-add-a-new-document-part-to-a-package.md	✅Succeeded
docs/general/how-to-create-a-package.md	✅Succeeded
docs/general/how-to-get-the-contents-of-a-document-part-from-a-package.md	✅Succeeded
docs/general/how-to-remove-a-document-part-from-a-package.md	✅Succeeded
docs/general/how-to-replace-the-theme-part-in-a-word-processing-document.md	✅Succeeded
docs/general/how-to-search-and-replace-text-in-a-document-part.md	✅Succeeded
docs/general/introduction-to-markup-compatibility.md	✅Succeeded
docs/general/overview.md	✅Succeeded
docs/includes/word/structure.md	✅Succeeded
docs/presentation/how-to-add-a-comment-to-a-slide-in-a-presentation.md	✅Succeeded
docs/presentation/how-to-apply-a-theme-to-a-presentation.md	✅Succeeded
docs/presentation/how-to-change-the-fill-color-of-a-shape-in-a-presentation.md	✅Succeeded
docs/presentation/how-to-create-a-presentation-document-by-providing-a-file-name.md	✅Succeeded
docs/presentation/how-to-delete-a-slide-from-a-presentation.md	✅Succeeded
docs/presentation/how-to-get-all-the-external-hyperlinks-in-a-presentation.md	✅Succeeded
docs/presentation/how-to-get-all-the-text-in-all-slides-in-a-presentation.md	✅Succeeded
docs/presentation/how-to-get-all-the-text-in-a-slide-in-a-presentation.md	✅Succeeded
docs/presentation/how-to-get-the-titles-of-all-the-slides-in-a-presentation.md	✅Succeeded
docs/presentation/how-to-insert-a-new-slide-into-a-presentation.md	✅Succeeded
docs/presentation/how-to-move-a-paragraph-from-one-presentation-to-another.md	✅Succeeded
docs/presentation/how-to-move-a-slide-to-a-new-position-in-a-presentation.md	✅Succeeded
docs/presentation/how-to-open-a-presentation-document-for-read-only-access.md	✅Succeeded
docs/presentation/how-to-retrieve-the-number-of-slides-in-a-presentation-document.md	✅Succeeded
docs/presentation/overview.md	✅Succeeded

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