Remove unreachable "otp_code" auth method

[aduth]

🛠 Summary of changes

Removes an unused reference to "otp_code" as a multi_factor_auth_method value, in order to avoid confusion for a value that's never logged.

I stumbled across this when searching possible multi_factor_auth_method values in the codebase. After verifying there are no results in CloudWatch for filter properties.event_properties.multi_factor_auth_method = 'otp_code', I noticed that this would be unused, due to how the form's extra analytics are overridden:

identity-idp/app/controllers/two_factor_authentication/otp_verification_controller.rb

Line 129 in fb94aad

properties = result.to_h.merge(analytics_properties)

identity-idp/app/controllers/two_factor_authentication/otp_verification_controller.rb

Lines 151 to 156 in fb94aad

	def analytics_properties
	parsed_phone = Phonelib.parse(phone)
	{
	context: context,
	multi_factor_auth_method: params[:otp_delivery_preference],

📜 Testing Plan

This is a refactor expected to be covered by existing test coverage.

rspec spec/controllers/two_factor_authentication/otp_verification_controller_spec.rb spec/forms/otp_verification_form_spec.rb

You could also verify that MFA'ing with a phone continues to log events with multi_factor_auth_method equal to the delivery method of your authenticator ("sms" or "voice").