Remove unused header file include due to fix build error (#142)

Author: Watson1978

ext/io/event/worker_pool_test.c

@@ -9,7 +9,6 @@
 #include <string.h>
 
 #include <unistd.h>
-#include <sys/select.h>
 #include <errno.h>
 #include <time.h>