Removed dead code from ngx_http_set_keepalive().

The code removed became dead after 98f03cd8d6cc (0.8.14),
circa when the request reference counting was introduced.

src/http/ngx_http_request.c

diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
index 204a939..5ee9dee 100644
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -3039,13 +3039,6 @@
 
     ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0, "set http keepalive handler");
 
-    if (r->discard_body) {
-        r->write_event_handler = ngx_http_request_empty_handler;
-        r->lingering_time = ngx_time() + (time_t) (clcf->lingering_time / 1000);
-        ngx_add_timer(rev, clcf->lingering_timeout);
-        return;
-    }
-
     c->log->action = "closing request";
 
     hc = r->http_connection;