Allow using auth_devise with discard

paranoia is not required anymore since 3.0 ships without it.
Who is using older versions of Solidus will see the deprecation
as the rest of the paranoia code in core.

app/models/spree/user.rb

@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 
-require 'paranoia'
-
 module Spree
   class User < Spree::Base
     include UserMethods
@@ -10,8 +8,18 @@ class User < Spree::Base
            :rememberable, :trackable, :validatable, :encryptable
     devise :confirmable if Spree::Auth::Config[:confirmable]
 
-    acts_as_paranoid
+    if defined?(Spree::SoftDeletable)
+      include Spree::SoftDeletable
+    else
+      acts_as_paranoid
+      include Spree::ParanoiaDeprecations
+
+      include Discard::Model
+      self.discard_column = :deleted_at
+    end
+
     after_destroy :scramble_email_and_password
+    after_discard :scramble_email_and_password
 
     def password=(new_password)
       generate_spree_api_key if new_password.present? && spree_api_key.present?

solidus_auth_devise.gemspec

@@ -40,7 +40,6 @@ Gem::Specification.new do |s|
   s.add_dependency "deface", "~> 1.0"
   s.add_dependency "devise", '~> 4.1'
   s.add_dependency "devise-encryptable", "0.2.0"
-  s.add_dependency "paranoia", "~> 2.4"
   s.add_dependency "solidus_core", solidus_version
   s.add_dependency "solidus_support", "~> 0.5"
 

spec/models/user_spec.rb

@@ -50,18 +50,8 @@
   end
 
   describe '#destroy' do
-    # Users with orders are not deletable in Solidus core
-    # therefore we cannot test this behaviour here.
-    # Also there are already sufficient specs in core.
     let(:user) { create(:user) }
 
-    it 'acts_as_paranoid' do
-      # Instead of testing implementation details of `acts_as_paranoid`
-      # we are testing that we are using `acts_as_paranoid` by using duck typing
-      expect(described_class).to respond_to(:with_deleted)
-      expect(user).to respond_to(:deleted_at)
-    end
-
     context 'with same email address as previously deleted account' do
       it 'will allow users to register later' do
         user1 = build(:user)
@@ -72,13 +62,27 @@
         expect(user2.save).to be false
         expect(user2.errors.messages[:email].first).to eq "has already been taken"
 
-        user1.destroy
+        user1.discard
         expect(user2.save).to be true
       end
     end
   end
 
-  describe '#really_destroy!' do
+  describe '#destroy' do
+    let(:user) { create(:user) }
+
+    it 'removes the record from the database' do
+      user.destroy
+
+      if defined?(Spree::ParanoiaDeprecations)
+        expect(Spree::User.with_discarded.exists?(id: user.id)).to eql true
+      else
+        expect(Spree::User.with_discarded.exists?(id: user.id)).to eql false
+      end
+    end
+  end
+
+  describe '#really_destroy!', if: defined?(Spree::ParanoiaDeprecations) do
     let(:user) { create(:user) }
 
     it 'removes the record from the database' do