docker: do not mention instance-config.php in leftypol dockerfile

docker/php/Dockerfile

@@ -82,9 +82,7 @@ COPY . /code
 # Make the instance configuration owned by www-data.
 # Make it writable by php.
 # Install the compose depedencies.
-RUN chown www-data /code/inc/instance-config.php && chgrp www-data /code/inc/instance-config.php \
-    && chmod 660 /code/inc/instance-config.php \
-    && cd /code && composer install
+RUN cd /code && composer install
 
 WORKDIR "/var/www"
 CMD [ "bootstrap.sh" ]