Remove unneeded header files from source files throughout.

winsup/cygwin/fhandler_disk_file.cc

@@ -10,16 +10,11 @@ Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
 details. */
 
 #include "winsup.h"
-#include <unistd.h>
 #include <stdlib.h>
-#include <sys/cygwin.h>
 #include <sys/acl.h>
 #include <sys/statvfs.h>
-#include <signal.h>
 #include "cygerrno.h"
-#include "perprocess.h"
 #include "security.h"
-#include "cygwin/version.h"
 #include "path.h"
 #include "fhandler.h"
 #include "dtable.h"
@@ -27,8 +22,6 @@ details. */
 #include "shared_info.h"
 #include "pinfo.h"
 #include "ntdll.h"
-#include <assert.h>
-#include <ctype.h>
 #include <winioctl.h>
 
 #define _COMPILING_NEWLIB