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.

lib/mix/tasks/pleroma/instance.ex

@@ -36,9 +36,7 @@ defmodule Mix.Tasks.Pleroma.Instance do
           listen_port: :string,
           strip_uploads: :string,
           anonymize_uploads: :string,
-          dedupe_uploads: :string,
-          skip_release_env: :boolean,
-          release_env_file: :string
+          dedupe_uploads: :string
         ],
         aliases: [
           o: :output,
@@ -243,24 +241,6 @@ defmodule Mix.Tasks.Pleroma.Instance do
 
       write_robots_txt(static_dir, indexable, template_dir)
 
-      if Keyword.get(options, :skip_release_env, false) do
-        shell_info("""
-        Release environment file is skip. Please generate the release env file before start.
-        `MIX_ENV=#{Mix.env()} mix pleroma.release_env gen`
-        """)
-      else
-        shell_info("Generation the environment file:")
-
-        release_env_args =
-          with path when not is_nil(path) <- Keyword.get(options, :release_env_file) do
-            ["gen", "--path", path]
-          else
-            _ -> ["gen"]
-          end
-
-        Mix.Tasks.Pleroma.ReleaseEnv.run(release_env_args)
-      end
-
       shell_info(
         "\n All files successfully written! Refer to the installation instructions for your platform for next steps."
       )