python: remove stale python2-config symbolic link

We already remove python2.7-config and the symbolic link
python-config, but we forgot to remove the python2-config symbolic
link.

Note that we can't use the <pkg>_CONFIG_SCRIPTS mechanism here because
python2.7-config is written in... Python, and doesn't follow the usual
syntax of <pkg>-config scripts. It takes the paths directly from
distutils.sysconfig.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>