[Chronik] ReverseLookup: Remove redundant lookup_cf_name

Summary: This has always been in the generic param L already, so we can just use that.

Test Plan: ninja check-crates && ninja check-functional

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D15547