bench: remove dead and buggy code

Pipe accept benchmarks have never been implemented, remove the code path.

Said code path also contained a bug: it tried to bind to the same pipe that is
bound to a few lines down.

test/benchmark-multi-accept.c

@@ -204,10 +204,6 @@ static void send_listen_handles(uv_handle_type type,
     ASSERT(0 == uv_tcp_init(loop, (uv_tcp_t*) &ctx.server_handle));
     ASSERT(0 == uv_tcp_bind((uv_tcp_t*) &ctx.server_handle, listen_addr));
   }
-  else if (type == UV_NAMED_PIPE) {
-    ASSERT(0 == uv_pipe_init(loop, (uv_pipe_t*) &ctx.server_handle, 0));
-    ASSERT(0 == uv_pipe_bind((uv_pipe_t*) &ctx.server_handle, IPC_PIPE_NAME));
-  }
   else
     ASSERT(0);