hw/arm/virt: Remove VirtMachineClass::claim_edge_triggered_timers field
The VirtMachineClass::claim_edge_triggered_timers field
was only used by virt-2.8 machine, which got removed.
Remove it and simplify fdt_add_timer_nodes() and build_gtdt().
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org> Reviewed-by: Thomas Huth <thuth@redhat.com> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>