mpl 3.4 drops font_manager._rebuild() function and breaks design imports

[bolliger32]

Description

Our CI pipeline just broke and it's b/c matplotlib just released v3.4.0. In this version there is no more _rebuild() function within the matplotlib.font_manager module. We call this function here:

rhg_compute_tools/rhg_compute_tools/design/__init__.py

Line 29 in 49d9f7b

from matplotlib.font_manager import _rebuild

It looks like the font loading lines above L129 are all commented out, so do we need this anymore? It wasn't immediately clear to me why matplotlib took it out or what the proper way to rebuild the font cache is now, but if we don't need it anymore we could remove that line. Until then, it's blocking as it breaks our CI

@delgadom do you know if we still need that _rebuild call?

[delgadom]

dang. no we don't