Remove unneeded header files from source files throughout.

winsup/cygwin/shm.cc

@@ -9,18 +9,13 @@ Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
 details. */
 
 #include "winsup.h"
-#include "cygerrno.h"
-#include <signal.h>
 #ifdef USE_SERVER
-#include <sys/types.h>
 #include <sys/queue.h>
-#include <stdio.h>
 #include <unistd.h>
 
 #include "pinfo.h"
 #include "sigproc.h"
 
-#include "cygserver_ipc.h"
 #include "cygserver_shm.h"
 #include "cygtls.h"
 #include "sync.h"