rate limiter: disable based on if remote ip was found, not on if the plug was enabled

The current rate limiter disable logic won't trigger when the remote ip
is not forwarded, only when the remoteip plug is not enabled, which is
not the case on most instances since it's enabled by default. This
changes the behavior to warn and disable  when the remote ip was not forwarded,
even if the RemoteIP plug is enabled.

Also closes #1620

config/test.exs

@@ -92,6 +92,8 @@ config :pleroma, :modules, runtime_dir: "test/fixtures/modules"
 
 config :pleroma, Pleroma.Emails.NewUsersDigestEmail, enabled: true
 
+config :pleroma, Pleroma.Plugs.RemoteIp, enabled: false
+
 if File.exists?("./config/test.secret.exs") do
   import_config "test.secret.exs"
 else