User: Don't error out when following a user that's already followed.

This leads to a few situations where it is impossible to follow a user.

lib/pleroma/user.ex

@@ -370,8 +370,8 @@ defmodule Pleroma.User do
     ap_followers = followed.follower_address
 
     cond do
-      following?(follower, followed) or info.deactivated ->
-        {:error, "Could not follow user: #{followed.nickname} is already on your list."}
+      info.deactivated ->
+        {:error, "Could not follow user: You are deactivatedt."}
 
       deny_follow_blocked and blocks?(followed, follower) ->
         {:error, "Could not follow user: #{followed.nickname} blocked you."}