Fix Type 3 font warning

While saving real-life plots to PDF, matplotlib emits the following warning:

'NimbusSanL-BolIta.otf' can not be subsetted into a Type 3 font. The entire font will be embedded in the output.
'NimbusSanL-Reg.otf' can not be subsetted into a Type 3 font. The entire font will be embedded in the output.

This is quite annoying and there might be a potential size improvement.