exec: housekeeping (funny since 02d0e095)

applied using ./scripts/clean-includes

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>