Refactor fee_grant AnteHandler to x/auth

[clevinson]

We shouldn't be maintaining two separate antehandler chains.

Ideally the x/fee_grant antehandler chain should be migrated over to x/auth AnteHandler chain.

[aaronc]

And if fee grant isn't in the AnteHandler constructor then we don't include it's AnteDecorator.

We may want to consider migrating to an AnteHandlerBuilder type rather than adding more positional parameters to the ante handler constructor.