nginx: use build defaults for user/pid settings

This varies based on the OS and packaging. It's best to make the
assumption that it's a reasonable nginx package rather than reducing
portability.

nginx/nginx.conf

@@ -2,10 +2,8 @@
 
 load_module modules/ngx_http_brotli_static_module.so;
 
-user nginx;
 worker_processes auto;
 worker_rlimit_nofile 16384;
-pid /run/nginx.pid;
 
 events {
     worker_connections 4096;