remove admin tasks as they have their page in mix tasks category already

docs/admin/admin_tasks.md

-# Admin tasks
-## Important
-
-If your instance is running in prod mode (most likely it is) make sure to prefix every command with `MIX_ENV=prod`.
-
-## User management
-
-It is possible to obtain a list of all available tasks with their options by executing `mix help pleroma.user`
-
-### Adding users
-
-Use `mix pleroma.user invite` to generate an invite link for a new user.
-
-Also, `mix pleroma.user new NICKNAME EMAIL [OPTION...]` can be used to register an account.
-
-### Making a user a moderator/admin/locked
-
-Run `mix pleroma.user set username --[no-]moderator` to make user a moderator or remove the moderator status.
-
-To make the user admin or locked use `mix pleroma.user set NICKNAME --[no-]admin` and `mix pleroma.user set NICKNAME --[no-]locked` respectively
-
-### Resetting a password
-
-Run `mix pleroma.user reset_password NICKNAME` to generate a password reset link that you can then send to the user.
-
-### Banning users
-
-Run `mix pleroma.user rm NICKNAME` to remove a local account.
-
-To deactivate(block from the server completely)/reactivate local and remote user accounts run:
-
-`mix pleroma.user toggle_activated NICKNAME@instancename`
-
-## Relay managment
-
-It is possible to obtain a list of all available tasks with their options by executing `mix help pleroma.relay`
-
-### Following a relay
-
-Run `mix pleroma.relay follow RELAY_URL`
-
-### Unfollowing a relay
-
-Run `mix pleroma.relay unfollow RELAY_URL`