exec: Remove unneeded include files

This file does not depend on windows.h.
Signed-off-by: NStefan Weil <sw@weilnetz.de>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NAndreas Färber <afaerber@suse.de>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

exec.c

@@ -17,9 +17,7 @@
  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  */
 #include "config.h"
-#ifdef _WIN32
-#include <windows.h>
-#else
+#ifndef _WIN32
 #include <sys/types.h>
 #include <sys/mman.h>
 #endif