This patch removes the signal handling in the webhook code.
With this code the syslog-ng process can no longer handle the SIGTERM and SIGINT signals.

For example when the following config is used:

@version: current
@include "scl.conf"
source s_webhook_source {
    file("/tmp/src.txt");
};
destination d_file {
    file("/tmp/dst.txt");
};
log {
    source(s_webhook_source);
    destination(d_file);
    flags(flow-control);
};

and syslog-ng is ran by systemd and systemctl stop syslog-ng is requested syslog-ng will ignore the SIGTERM signal all together which will cause systemd to kill the process due to the failed timeout of the shutdown, this patch fixes this