Function pallet_proxy::migration::migrate_to_time_delayed_proxies

pub fn migrate_to_time_delayed_proxies<T: Config>() -> Weight

Migration code for https://github.com/paritytech/substrate/pull/6770

Details: This migration was introduced between Substrate 2.0-RC6 and Substrate 2.0 releases. Before this migration, the Proxies storage item used a tuple of AccountId and ProxyType to represent the proxy definition. After #6770, we switched to use a struct ProxyDefinition which additionally included a BlockNumber delay value. This function, simply takes any existing proxies using the old tuple format, and migrates it to the new struct by setting the delay to zero.