Merge "base: drop not needed Linaro OBS key"

docker/base/Dockerfile.j2

@@ -370,7 +370,6 @@ COPY apt_preferences.{{ base_distro }} /etc/apt/preferences
       '4D1BB29D63D98E422B2113B19334A25F8507EFA5',
     ] %}
     {% set remote_apt_keys = [
-      'http://obs.linaro.org/ERP:/18.06/Debian_9/Release.key',
       'https://download.docker.com/linux/debian/gpg',
       'https://packages.grafana.com/gpg.key'
     ] %}