cubicweb-brainomics #3486002 Drop leftover bootstrap css in uiprops [validation pending]

Css should be correctly dropped in Uiprops.

prioritynormal
typebug
done in0.7.1
load0.100
load left0.000
closed by#b78f30074468 [uiprops] Remove call to bootstrap.css, closes #3486002
patch[uiprops] Remove call to bootstrap.css, closes #3486002 [applied]