Pleroma.ApplicationRequirements: fix dialyzer errors

lib/pleroma/application_requirements.ex:19:unknown_type
Unknown type: Pleroma.ApplicationRequirements.VerifyError.t/0.

lib/pleroma/application_requirements.ex:199:pattern_match_cov
The pattern
variable_result

can never match, because previous clauses completely cover the type
:ok.

lib/pleroma/application_requirements.ex

@@ -7,7 +7,10 @@ defmodule Pleroma.ApplicationRequirements do
   The module represents the collection of validations to runs before start server.
   """
 
-  defmodule VerifyError, do: defexception([:message])
+  defmodule VerifyError do
+    defexception([:message])
+    @type t :: %__MODULE__{}
+  end
 
   alias Pleroma.Config
   alias Pleroma.Helpers.MediaHelper
@@ -193,8 +196,6 @@ defmodule Pleroma.ApplicationRequirements do
     end
   end
 
-  defp check_system_commands!(result), do: result
-
   defp check_repo_pool_size!(:ok) do
     if Pleroma.Config.get([Pleroma.Repo, :pool_size], 10) != 10 and
          not Pleroma.Config.get([:dangerzone, :override_repo_pool_size], false) do