buildsteps_feed.py: adopt buildbot to new cli
buildsteps_feed.py: adopt buildbot to new cli

In https://github.com/Freifunk-Spalter/repo_builder/pull/12 the
invocation of the repo_builder changed. Thus it can select the
right sdk-version by itself now.

Signed-off-by: Martin Hübner <dd5c834ccafc62f3f340ff4772747b4da2828695@web.de>

freifunk-berlin/buildbot