Fix various issues reported by Dializer

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/graphql/api/follows.ex

@@ -69,7 +69,8 @@ defmodule Mobilizon.GraphQL.API.Follows do
     )
 
     case Actors.check_follow(follower, followed) do
-      %Follower{approved: false} ->
+      %Follower{approved: false} = follow ->
+        Actors.delete_follower(follow)
         {:error, "Follow already rejected"}
 
       %Follower{} = follow ->