drivers: ieee802154_nrf5: Removed CSL placeholder window
drivers: ieee802154_nrf5: Removed CSL placeholder window

Since nRF IEEE 802.15.4 radio driver is now capable of calculating CSL
phase based on provided anchor time and CSL period, the CSL placeholder
window is no longer necessary. This commit removes it and switches to
the new calculation method.

Signed-off-by: Artur Hadasz <79b70aa689e4f0f8efb568478ebe43b92399495d@nordicsemi.no>
Signed-off-by: Jędrzej Ciupis <6236c7d07f3a915f3607d3bfbdd3ebf209c7426c@nordicsemi.no>

zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr