Removed unused method

This was used by the `UserApplicationPermissionPolicy`, which was
deleted in 2a78b5c

app/models/user_application_permission.rb

@@ -8,10 +8,6 @@ class UserApplicationPermission < ApplicationRecord
 
   before_validation :assign_application_id
 
-  def self.for(user:, supported_permission:, application: nil)
-    new(user:, supported_permission:, application: application || supported_permission.application)
-  end
-
 private
 
   # application_id is duplicated across supported_permissions and user_application_permissions

test/models/user_application_permission_test.rb

@@ -1,37 +1,6 @@
 require "test_helper"
 
 class UserApplicationPermissionTest < ActiveSupport::TestCase
-  context ".for" do
-    setup do
-      @user = build(:user)
-      @supported_permission = build(:supported_permission)
-      @application = build(:application, supported_permissions: [@supported_permission])
-    end
-
-    context "for a user, supported permission, and application" do
-      setup { @result = UserApplicationPermission.for(user: @user, supported_permission: @supported_permission, application: @application) }
-
-      should "return a UserApplicationPermission with the given associations" do
-        assert @result.instance_of?(UserApplicationPermission)
-        assert_equal @user, @result.user
-        assert_equal @supported_permission, @result.supported_permission
-        assert_equal @application, @result.application
-      end
-
-      should "not persist the UserApplicationPermission" do
-        assert_not @result.persisted?
-      end
-    end
-
-    context "without an application" do
-      should "infer the application from the supported permission" do
-        result = UserApplicationPermission.for(user: @user, supported_permission: @supported_permission)
-
-        assert_equal @application, result.application
-      end
-    end
-  end
-
   context "validations" do
     setup do
       @user = create(:user)