Remove release_env

While taking a final look at instance.gen before releasing I noticed
that the release_env task outputs messages in broken english. Upon
further inspection it seems to have even more severe issues which, in
my opinion, warrant it's at least temporary removal:
- We do not explain what it actually does, anywhere. Neither the task
 docs nor instance.gen, nor installation instructions.
- It does not respect FHS on OTP releases (uses /opt/pleroma/config even
 though we store the config in /etc/pleroma/config.exs).
- It doesn't work on OTP releases, which is the main reason it exists.
Neither systemd nor openrc service files for OTP include it.
- It is not mentioned in install guides other than the ones for Debian
and OTP releases.

installation/init.d/pleroma

@@ -8,7 +8,6 @@ pidfile="/var/run/pleroma.pid"
 directory=/opt/pleroma
 healthcheck_delay=60
 healthcheck_timer=30
-export $(cat /opt/pleroma/config/pleroma.env)
 
 : ${pleroma_port:-4000}
 

installation/pleroma.service

@@ -17,8 +17,6 @@ Environment="MIX_ENV=prod"
 Environment="HOME=/var/lib/pleroma"
 ; Path to the folder containing the Pleroma installation.
 WorkingDirectory=/opt/pleroma
-; Path to the environment file. the file contains RELEASE_COOKIE and etc 
-EnvironmentFile=/opt/pleroma/config/pleroma.env
 ; Path to the Mix binary.
 ExecStart=/usr/bin/mix phx.server