Bug 1874208 - Remove the always printed Site not up-to-date reason r=firefox-build-system-reviewers,glandium

While this message was sometimes useful to help troubleshoot for end
users, it's causing issues parsing `stdout` (since it can't use the mach
logging infrastructure due to being too early in the startup). We also
can't use `stderr` since some mozharness scripts treat any `stderr`
output as a full error.

Differential Revision: https://phabricator.services.mozilla.com/D198451

python/mach/mach/site.py

@@ -562,7 +562,6 @@ class CommandSiteManager:
         """
         result = self._up_to_date()
         if not result.is_up_to_date:
-            print(f"Site not up-to-date reason: {result.reason}")
             active_site = MozSiteMetadata.from_runtime()
             if active_site.site_name == self._site_name:
                 print(result.reason, file=sys.stderr)