`lightning_invoice::utils` Should use a different logger/keysinterface than the ChannelManager ones

[TheBlueMatt]

ChannelManager's Logger and KeysInterface have to be owned, ie for the sample have to be a full Arc. In the utils methods, there's no need for an owned reference, as the function doesn't need to hold the reference longer than itself. Thus, tying the L and K bounds as being the same as the equivalent bounds on the ChannelManager is overly restrictive.