Revert "Make BG(syslog_device) per request"

Revert "Make BG(syslog_device) per request"

This reverts commit b0d7b126a29a1972229ac91d6d28f5331912eddb.

This change wasn't quite right: I noticed only now that the
RSHUTDOWN function is #ifdef PHP_WIN32 and I'm not fully convinced
that ifdef can be removed: syslog might also be used by error
logging in FPM for example, in which case we probably shouldn't
be closing the log here.

Generally it's unclear how the openlog() functionality exposed
by PHP is supposed to interact with openlog() uses by SAPIs.

For now I'll just revert this change and let it leak across
requests.