Remove unused authentication generator file

[jeromedalbert]

Follow-up to #542.

Remove the unused lib/generators/factory_bot/authentication/templates/users.rb file.

When using the authentication generator, we generate a users.rb file with the following values:

factory_bot_rails/lib/generators/factory_bot/authentication/authentication_generator.rb

Lines 14 to 19 in dfdef4c

	def attributes
	[
	FixedAttribute.new(:email_address, "[email protected]"),
	FixedAttribute.new(:password, "password")
	]
	end

And this is expected behavior:

factory_bot_rails/features/generators.feature

Lines 102 to 110 in dfdef4c

	And the file "spec/factories/users.rb" should contain exactly:
	"""
	FactoryBot.define do
	factory :user do
	email_address { "[email protected]" }
	password { "password" }
	end
	end
	"""

So the values of lib/generators/factory_bot/authentication/templates/users.rb are never used. This cleanup PR removes the file.