cubicweb #3799117 remove pre 3.12 bw compat [validation pending]

prioritynormal
typeenhancement
done in3.20.0
load0.200
load left0.000
closed by#727bbb361ed1 remove 3.11 bw compat
patch[doc/3.20] more details on removed code [applied]remove 3.11 bw compat [applied]remove most 3.10 bw compat [applied]