Revert "docs: promote SoftwareUpdater as easy tool to update Haiku."
This reverts commit c4b4f84bade59a23044f507e8f68b8c8c9e9fe11.
This reverts commit 35941876c819fdfa980c423f089b10e2301692e2.
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The Userguide and Welcome Guide are written and managed in the Userguide
Translator, not in the tree.