Remove PM2 guide (#4991)

There's apparently no way to specify exit codes
for which the process should not be restarted.

This just shows how poor of a process manager PM2 is
so we really should not continue to recommend it in the documentation...

Ref:
https://stackoverflow.com/questions/43614017/how-to-only-restart-node-process-with-pm2-if-exit-code-0

docs/autostart_pm2.rst

@@ -1,56 +0,0 @@
-.. pm2 service guide
-
-==============================================
-Setting up auto-restart using pm2 on Linux
-==============================================
-
-.. note:: This guide is for setting up PM2 on a Linux environment. This guide assumes that you already have a working Red instance.
-
---------------
-Installing PM2
---------------
-
-Start by installing Node.JS and NPM via your favorite package distributor. From there run the following command:
-
-.. prompt:: bash
-
-    npm install pm2 -g
-
-After PM2 is installed, run the following command to enable your Red instance to be managed by PM2. Replace the brackets with the required information.
-You can add additional Red based arguments after the instance name, such as :code:`--dev`.
-
-.. prompt:: bash
-
-    pm2 start "<path>" --name "<app_name>" -- -O -m redbot <instance_name> --no-prompt
-
-**Arguments to replace**
-
-- ``<app_name>`` - A name to identify the bot within pm2, this is not your Red instance.
-
-- | ``<path>`` - The location of your Python interpreter.
-  | To find out where that is, use the proper set of commands:
-
-  .. prompt:: bash
-      :prompts: $,(redenv) $
-      :modifiers: auto
-
-      # If redbot is installed in a venv
-      $ source ~/redenv/bin/activate
-      (redenv) $ which python
-
-      # If redbot is installed in a pyenv virtualenv
-      $ pyenv shell <virtualenv_name>
-      (redenv) $ pyenv which python
-
-- ``<instance_name>`` - The name of your Red instance.
-
-------------------------------
-Ensuring that PM2 stays online
-------------------------------
-
-To make sure that PM2 stays online and persistence between machine restarts, run the following commands:
-
-.. prompt:: bash
-
-    pm2 save
-    pm2 startup

docs/index.rst

@@ -19,7 +19,6 @@ Welcome to Red - Discord Bot's documentation!
     about_venv
     autostart_systemd
     autostart_mac
-    autostart_pm2
 
 .. toctree::
     :maxdepth: 2