[chronik] remove outdated comment for enable_lokad_id_index
Summary: enable_lokad_id_index_specified does not exist in the final post-review version of D15921
Test Plan: NA, doc change only
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D16866