Revert "Custom mix task to retry failed tests once in CI pipeline"

This reverts commit ed2976b237.

lib/mix/tasks/pleroma/test_runner.ex

@@ -1,25 +0,0 @@
-defmodule Mix.Tasks.Pleroma.TestRunner do
-  @shortdoc "Retries tests once if they fail"
-
-  use Mix.Task
-
-  def run(args \\ []) do
-    case System.cmd("mix", ["test"] ++ args, into: IO.stream(:stdio, :line)) do
-      {_, 0} ->
-        :ok
-
-      _ ->
-        retry(args)
-    end
-  end
-
-  def retry(args) do
-    case System.cmd("mix", ["test", "--failed"] ++ args, into: IO.stream(:stdio, :line)) do
-      {_, 0} ->
-        :ok
-
-      _ ->
-        exit(1)
-    end
-  end
-end