[Services] Remove build_services compatibility logic

Summary:
This largely undoes the compatibility logic in D4734 to make
gates pass.

Since blob, backup, and tunnelbroker have been updated, there's no reason to
use the legacy "special paths" docker-specific workflow

Test Plan: Blob, Backup, and Tunnelbroker gates pass

Reviewers: abosh, atul, max, karol

Reviewed By: abosh, atul

Subscribers: ashoat, tomek, adrian

Differential Revision: https://phab.comm.dev/D4735