Revert "DEV: Use 127.0.0.1 instead of localhost as Capybara's server host (#27215)" (#27218)

This reverts commit 998b50fdf4.

Ended up making system tests even more unstable

spec/system/user_page/user_preferences_security_spec.rb

@@ -8,9 +8,6 @@ describe "User preferences | Security", type: :system do
   let(:user_menu) { PageObjects::Components::UserMenu.new }
 
   before do
-    @original_host = Capybara.server_host
-    SiteSetting.force_hostname = Capybara.server_host = "localhost"
-
     user.activate
     # testing the enforced 2FA flow requires a user that was created > 5 minutes ago
     user.created_at = 6.minutes.ago
@@ -21,8 +18,6 @@ describe "User preferences | Security", type: :system do
     DiscourseWebauthn.stubs(:origin).returns(current_host + ":" + Capybara.server_port.to_s)
   end
 
-  after { SiteSetting.force_hostname = Capybara.server_host = @original_host }
-
   shared_examples "security keys" do
     it "adds a 2FA security key and logs in with it" do
       options = ::Selenium::WebDriver::VirtualAuthenticatorOptions.new