Fix always remove pids on boot
Further info: https://github.com/discourse/discourse_docker/commit/ca39457ffc10c8eedc9843fe541a7265cc4e888c
Nowadays, we specify the UNICORN_PIDS_PATH as env variable, concretly to /discourse/tmp/pids/. This comes by default in the unicorn.rb.
We will need to get rid off of the UNICORN_PIDS_PATH env variable for all instances.