The `SkipCheckifFeeless::IDENTIFIER` became transparent (ie was whatever
the inner signed ext was). This PR just makes the `TypeInfo` transparent
too, so that libraries that use said info to decode the data (ie subxt)
can behave identically whether or not the `SkipCheckifFeeless` wrapper
is used or not.

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Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>