semaphore: drop the custom Python 3.6 PPA

Shouldn't be needed anymore, since the new Sempahore supports Ubuntu
Bionic

Author: mrc0mmand

test/semaphore-run

@@ -19,11 +19,7 @@ set -eu
 (
     set -x
 
-    sudo rm /etc/apt/sources.list.d/*
-
     sudo apt install -y software-properties-common
-    sudo add-apt-repository -y ppa:jonathonf/python-3.6
-    sudo add-apt-repository -y ppa:ginggs/backports
     sudo apt -y update
     sudo apt -y --no-install-recommends install \
          python3.6 \