log: don't log to qubes.log file on disk, only stderr

stderr already ends goes to syslog. Stop duplicating the messages to
/var/lib/qubes/qubes.log (or /tmp/qubes.log), so logrotate doesn't have
to restart qubesd - causing problems such as aborted backups.

Fixes QubesOS/qubes-issues#5004

linux/system-config/logrotate-qubes

@@ -6,14 +6,6 @@
     endscript
 }
 
-/var/log/qubes/qubes.log {
-    create 0640 root qubes
-    su root qubes
-    postrotate
-        /bin/systemctl restart qubesd.service >/dev/null 2>/dev/null || true
-    endscript
-}
-
 /var/log/qubes/vm-*.log {
     su root qubes
 }

qubes/app.py

@@ -1486,7 +1486,7 @@ def on_domain_pre_deleted(self, event, vm):
                         raise qubes.exc.QubesVMInUseError(
                             vm,
                             'Domain is in use: {!r};'
-                            'see /var/log/qubes/qubes.log in dom0 for '
+                            "see 'journalctl -u qubesd -e' in dom0 for "
                             'details'.format(
                                 vm.name))
                 except AttributeError:

qubes/log.py

@@ -95,21 +95,6 @@ def enable():
     handler_console.setFormatter(formatter_console)
     logging.root.addHandler(handler_console)
 
-    if os.path.exists('/var/log/qubes'):
-        log_path = '/var/log/qubes/qubes.log'
-    else:
-        # for tests, travis etc
-        log_path = '/tmp/qubes.log'
-    old_umask = os.umask(0o007)
-    try:
-        handler_log = logging.FileHandler(log_path, 'a', encoding='utf-8')
-        fcntl.fcntl(handler_log.stream.fileno(),
-            fcntl.F_SETFD, fcntl.FD_CLOEXEC)
-    finally:
-        os.umask(old_umask)
-    handler_log.setFormatter(formatter_log)
-    logging.root.addHandler(handler_log)
-
     logging.root.setLevel(logging.INFO)
 
 def enable_debug():