[matplotlib-devel] remove old branches

[Thomas C. <tca...@gm...>]

Does anyone protest to removing all of the branches from the main repo
except:

 - master
 - v1.4.x
 - v1.4.2-doc

Having old branches around can lead to confusion (see
https://github.com/matplotlib/matplotlib/pull/3748#issuecomment-61372162).

Tom