Remove unneeded ENV, we already have it in base image

Change-Id: I93d700beab0254cfcabffb37b6b406bcb2c172ab

docker/base-tools/Dockerfile.j2

@@ -1,8 +1,6 @@
 FROM {{ namespace }}/base:{{ tag }}
 MAINTAINER {{ maintainer }}
 
-# This will prevent questions from being asked during the install
-ENV DEBIAN_FRONTEND noninteractive
 COPY requirements.txt /tmp/requirements.txt
 
 RUN apt-get install -y --no-install-recommends netcat lvm2 open-iscsi tgt vim less patch gcc python-dev \