Remove unused excessUTXOCharge config option

Summary:
The argument and command line option are set but never used.
It is therefore very unlikely that anyone requires the RPC outputs to be set, so I think we can skip the deprecation process for this one.

Ref D962, D963, D1372

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14888