remove unused includes

This patch removes includes that are not used. The removals were found with
include-what-you-use which checks if any of the symbols from a header is
in use.

src/activate/activate.c

@@ -20,7 +20,6 @@
 ***/
 
 #include <unistd.h>
-#include <fcntl.h>
 #include <sys/epoll.h>
 #include <sys/prctl.h>
 #include <sys/socket.h>