Revert "Use tini as PID 1 inside the container"

This reverts commit 31d6d84.

While tini successfully forwards signals, this leads to `runuser`
killing prosody now. The container does terminate in 10 seconds, so
Docker is happy and you could argue that actually fixes prosody#68, but it's no
graceful shutdown. The revert is done because it's easier to apply a
real fix without tini.

Dockerfile

@@ -30,7 +30,6 @@ RUN apt-get update \
         openssl \
         ca-certificates \
         ssl-cert \
-        tini \
     && rm -rf /var/lib/apt/lists/*
 
 # Install and configure prosody

entrypoint.sh

@@ -10,12 +10,12 @@ if [[ "$(stat -c %u /var/run/prosody/)" != "$data_dir_owner" ]]; then
 fi
 
 if [[ "$1" != "prosody" ]]; then
-    exec tini -- prosodyctl "$@"
+    exec prosodyctl "$@"
     exit 0;
 fi
 
 if [[ "$LOCAL" && "$PASSWORD" && "$DOMAIN" ]]; then
     prosodyctl register "$LOCAL" "$DOMAIN" "$PASSWORD"
 fi
 
-exec tini -- runuser -u prosody -- "$@"
+exec runuser -u prosody -- "$@"