rip out fetch_initial_posts

Every time someone tries to use it, it goes mad and tries to scrape the
entire fediverse for no visible reason, it's better to just remove it
than continue shipping it in it's current state.

idea acked by lain and feld on irc

Closes #1595 #1422

priv/repo/migrations/20200314123607_config_remove_fetch_initial_posts.exs

@@ -0,0 +1,10 @@
+defmodule Pleroma.Repo.Migrations.ConfigRemoveFetchInitialPosts do
+  use Ecto.Migration
+
+  def change do
+    execute(
+      "delete from config where config.key = ':fetch_initial_posts' and config.group = ':pleroma';",
+      ""
+    )
+  end
+end

priv/repo/migrations/20200315125756_delete_fetch_initial_posts_jobs.exs

@@ -0,0 +1,10 @@
+defmodule Pleroma.Repo.Migrations.DeleteFetchInitialPostsJobs do
+  use Ecto.Migration
+
+  def change do
+    execute(
+      "delete from oban_jobs where worker = 'Pleroma.Workers.BackgroundWorker' and args->>'op' = 'fetch_initial_posts';",
+      ""
+    )
+  end
+end