cubicweb #17069762 cwctl: do only remove data dir content in gen_static_datadir (and upgrade) [done]

these commands should not remove the data directory iteself, only its content

prioritynormal
typebug
done in<not specified>
load left0.000
closed by#20035170160c [cwctl] do only clean static data dir content (closes #17069762)
patch[cwctl] do only clean static data dir content (closes #17069762) [applied]