kernel: remove event_t as it suffered from a lost wakeup issue

kernel-src/include/kernel/net.h

@@ -6,7 +6,6 @@
 
 #include <hashtable.h>
 #include <mutex.h>
-#include <event.h>
 #include <string.h>
 #include <arch/cpu.h>
 #include <kernel/abi.h>

kernel-src/include/kernel/pipefs.h

@@ -4,7 +4,6 @@
 #include <kernel/vfs.h>
 #include <ringbuffer.h>
 #include <semaphore.h>
-#include <event.h>
 #include <kernel/poll.h>
 
 typedef struct pipenode_t {