target/arm: Remove timer_del()/timer_deinit() before timer_free()

The Arm CPU finalize function uses a sequence of timer_del(), timer_deinit(),
timer_free() to free the timer. The timer_deinit() step in this was always
unnecessary, and now the timer_del() is implied by timer_free(), so we can
collapse this down to simply calling timer_free().

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201215154107.3255-5-peter.maydell@linaro.org