Reverts Hello Dolly changes moving the plugin to a containing folder. Removes the `upgrade_690()` function in it's entirety as the upgrade routine is no longer required.
Fully reverted commits: [60666], [60670], [60716], [60725]; partially reverts [60721].
Porps johnbillion, whyisjake, SirLouen, mindctrl, afragen, jorbin, Otto42, swissspidy, welcher, davidbaumwald.
See #53323.
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