enable system packages for proxygen (#542)

Summary:
Pull Request resolved: #542

update proxgen github builds to use system packages

github mac runners have python3.13 installed, which has removed the pipes module.  proxygen jobs were configured not to use the homebrew system packages, so it tried to build ninja from source, which fails as it uses pipes in its build script.  switching to system packages fixes it, plus makes the builds faster.

Reviewed By: jbeshay

Differential Revision: D67866148

fbshipit-source-id: 1c90e6eecced1d7208982f9568f67c1ec5a60077