Fix for np.float deprecation

[mbruckner-work]

Pairing code for TROPOMI NO2 used np.float in one line.
The np.float alias was deprecated in the Numpy 1.20.0 release (see https://numpy.org/devdocs/release/1.20.0-notes.html#deprecations).

[zmoon]

I did a brief search and saw cal_mod_no2col.py has some too, though they are commented out 🤷