[services][identity] clean up some redundancies

Summary: just some small refactors. not adding jim since this is a pretty trivial diff

Test Plan: ran cargo build

Reviewers: palys-swm, karol-bisztyga

Reviewed By: palys-swm

Subscribers: ashoat, Adrian, atul, yayabosh

Differential Revision: https://phab.comm.dev/D4279