CPython 3.1 branch is no longer maintained (#409)

plugins/python-build/share/python-build/3.1-dev

@@ -1,3 +0,0 @@
-#require_gcc
-install_package "readline-6.3" "http://ftpmirror.gnu.org/readline/readline-6.3.tar.gz#56ba6071b9462f980c5a72ab0023893b65ba6debb4eeb475d7a563dc65cafd43" standard --if has_broken_mac_readline
-install_hg "Python-3.1-dev" "https://bitbucket.org/mirror/cpython" "3.1" standard verify_py31 ensurepip