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

setup.py

@@ -1396,7 +1396,7 b' class RustExtension(Extension):'
 
             env['HOME'] = pwd.getpwuid(os.getuid()).pw_dir
 
-        cargocmd = ['cargo', 'rustc', '-vv', '--release']
+        cargocmd = ['cargo', 'rustc', '--release']
 
         feature_flags = []