ssl-certificate-expiry: remove hardcoded CA directory path

This should allow the plugin to be usable on all platforms.

plugins/ssl/ssl-certificate-expiry

@@ -123,7 +123,7 @@ print_expire_days() {
     [ -n "$starttls" ] && s_client_args="-starttls $starttls"
 
     # shellcheck disable=SC2086
-    echo "" | openssl s_client -CApath /etc/ssl/certs \
+    echo "" | openssl s_client \
             -servername "$host" -connect "${host}:${port}" \
             $s_client_args 2>/dev/null \
         | parse_valid_days_from_certificate