cubicweb #2558496 fix doc packaging for online deployment on cwo [done]

the online doc has been severely broken for months

prioritynormal
typebug
done in3.15.9
load1.000
load left0.000
closed by#2294fad830ca [packaging] don't compress txt files (closes #2558496), #67a5fccb802a [packaging] Fix search in squeeze cubicweb-documentation package (closes #2558496)