base: optimize size

Reduce 3 layers in the base image; Free up unused space, from 93.4MB to 86.3MB.

base/Dockerfile

@@ -4,19 +4,16 @@ ARG JITSI_RELEASE=stable
 
 ENV S6_BEHAVIOUR_IF_STAGE2_FAILS=2
 
-ADD https://github.com/just-containers/s6-overlay/releases/download/v1.22.1.0/s6-overlay-amd64.tar.gz /tmp/s6-overlay.tar.gz
-ADD https://download.jitsi.org/jitsi-key.gpg.key /tmp/jitsi.key
-ADD https://github.com/subchen/frep/releases/download/v1.3.5/frep-1.3.5-linux-amd64 /usr/bin/frep
-
 COPY rootfs /
 
 RUN \
-	tar xfz /tmp/s6-overlay.tar.gz -C / && \
-	rm -f /tmp/*.tar.gz && \
 	apt-dpkg-wrap apt-get update && \
 	apt-dpkg-wrap apt-get install -y apt-transport-https apt-utils ca-certificates gnupg && \
-	apt-key add /tmp/jitsi.key && \
-	rm -f /tmp/jitsi.key && \
+	apt-dpkg-wrap apt-get install -y wget && \
+	wget -qO - https://github.com/just-containers/s6-overlay/releases/download/v1.22.1.0/s6-overlay-amd64.tar.gz | tar xfz - -C / && \
+	wget -qO - https://download.jitsi.org/jitsi-key.gpg.key | apt-key add - && \
+	wget -q https://github.com/subchen/frep/releases/download/v1.3.5/frep-1.3.5-linux-amd64 -O /usr/bin/frep && \
+	apt-dpkg-wrap apt-get --purge remove -y wget && \
 	echo "deb https://download.jitsi.org $JITSI_RELEASE/" > /etc/apt/sources.list.d/jitsi.list && \
 	echo "deb http://ftp.debian.org/debian stretch-backports main" > /etc/apt/sources.list.d/backports.list && \
 	apt-dpkg-wrap apt-get update && \