Revert "docs: promote SoftwareUpdater as easy tool to update Haiku."
This reverts commit 6487273924d1546b57b1dad2573d1c1204e5ae22.
This reverts commit 8aab3a0d5ec8deceb0ad0bed99812bdd42e2bde7.
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The Userguide and Welcome Guide are written and managed in the Userguide
Translator, not in the tree.