cubicweb #3728904 Remove useless 'ui-cube' configuration option [validation pending]

Confusing and broken and useless.

prioritynormal
typebug
done in3.19.0
load0.100
load left0.000
closed by#283503f58400 [cwconfig] Remove useless 'ui-cube' configuration option (closes #3728904)
patch[cwconfig] Remove useless 'ui-cube' configuration option (closes #3728904) [applied]