cubicweb #15538383 Drop datafeed's cwxmlparser [validation pending]

It has been deprecated in 3.21 and hold a lot of code that could be removed / cleaned.

prioritynormal
typeenhancement
done in3.24.0
load left0.000
closed by#60fed6272771 [repository] Drop deprecated extid2eid API and friends
patch[repository] Drop deprecated extid2eid API and friends [applied]