#1114 highlighted some redundancy with regards to the contents of the default matplotlibrc file. There are at least 3 copies of a "default" matplotlibrc:

matplotlibrc.template
./lib/matplotlib/mpl-data/matplotlibrc
./doc/pyplots/matplotlibrc

Replace these with a single definitive source.

Additionally, investigate the use of lib/matplotlib/mpl-data/matplotlib.conf to confirm that it is still needed.