Remove Mime::Type#verify_request? and Mime::Type.browser_generated_types were deprecated.
Raise ArgumentError to fix Rails 4.1 deprecation warn message.
Remove behavior that deals with a string as third argument of `add_index`, because this was deprecated.

Some testcases is failed, so I replaced nil to empty hash in add_reference.
Remove instance level attr_readonly setting was deprecated.
Remove instance level serialized_attributes setting was deprecated.
Remove unnecessary testcase for instance level stored_attributes.
Merge pull request #10821 from kennyj/deprecations_4_1-2

Remove some deprecated methods in Rails 4.1 again.