feat(server): remove ulimit (Jigsaw-Code#1447)

This is unnecessarily restricting the server, which limits the number of connections we can support. It also can't raise the ulimit, since the host impose a cap on the container.

Service providers can still set the ulimit on their host if they want to.

src/shadowbox/docker/cmd.sh

@@ -20,25 +20,6 @@ export SB_METRICS_URL="${SB_METRICS_URL:-https://prod.metrics.getoutline.org}"
 # Make sure we don't leak readable files to other users.
 umask 0007
 
-# The maximum number of files that can be opened by ss-server greatly
-# influence on performance, as described here:
-#   https://shadowsocks.org/en/config/advanced.html
-#
-# The steps described in that page do *not* work for processes running
-# under Docker, at least on modern Debian/Ubuntu-like systems whose init
-# daemons allow per-service limits and ignore completely
-# /etc/security/limits.conf. On those systems, the Shadowbox container
-# will, by default, inherit the limits configured for the Docker service:
-#   https://docs.docker.com/engine/reference/commandline/run/#set-ulimits-in-container-ulimit
-#
-# Interestingly, we observed poor performance with large values such as 524288
-# and 1048576, the default values in recent releases of Ubuntu. Our
-# non-exhaustive testing indicates a performance cliff for Outline after values
-# around 270k; to stay well below of this cliff we've semi-handwaved-ly settled
-# upon a limit of 32k files.
-# shellcheck disable=SC2039 # ulimit -n is in bash and busybox but not POSIX
-ulimit -n 32768
-
 # Start cron, which is used to check for updates to the IP-to-country database
 crond