Explicitly ignore returned value from unlink() in ngx_open_tempfile().

The only thing we could potentially do here in case of error
returned is to complain to error log, but we don't have log
structure available here due to interface limitations.

Prodded by Coverity.

src/os/unix/ngx_files.c

@@ -139,7 +139,7 @@ ngx_open_tempfile(u_char *name, ngx_uint_t persistent, ngx_uint_t access)
               access ? access : 0600);
 
     if (fd != -1 && !persistent) {
-        unlink((const char *) name);
+        (void) unlink((const char *) name);
     }
 
     return fd;