Fix ugly kinematics

[scarlehoff]

In the new implementation, the kinematics have been left as they were in the old implementation. Without the magic plotoptions within validphys, some of these are ugly-ish in plot, like e.g., https://vp.nnpdf.science/EK2J-BJyRV2_zKT2-Zeoyg==/ where m^2 is used when it would be nicer to have m.

These doesn't have any effect anywhere (if the cuts are updated accordingly), so please, everyone, feel free to update the kinematic selection of any dataset you find produces ugly plots :)

• Use mass instead of masses square for DY (both FT and collider)
• Use Q instead of Q2 for DIS
• Remove sqrts from any dataset for which it is included in the name.