cubicweb #2777628 Drop iprogress code for good [validation pending]

Follow up to bug #1916016. iprogress has been in its own cube for 3 releases and is barely used.

Kill its remains with fire.

prioritynormal
typeenhancement
done in3.17.0
load0.500
load left0.000
closed by#86c1a5afbe4e Drop iprogress code (closes #2777628)
patchDrop iprogress code (closes #2777628) [applied]