setup: stop asking cargo to spam
It prints this kind of stuff by default:
Compiling regex v1.3.6 Compiling rand v0.7.3 Compiling crossbeam-deque v0.7.3
which is way better than we ask for before this change, which is
screen after screen of compilation commands and irrelevant warnings in
crates we use.
Differential Revision: https://phab.mercurial-scm.org/D8537