Update docs/porting/psa/spm.md

Co-Authored-By: danny4478 <[email protected]>

Author: Alexander Zilberkant

docs/porting/psa/spm.md

@@ -207,7 +207,6 @@ These are the guidelines you should follow if you have multicore systems:
 - For each core, initialize, configure and enable the a mailbox event (usually an interrupt) at `SystemInit()`.
 - For each core, implement the IPC event handler (usually interrupt handler):
   - This handler must call an Arm callback function. The [HAL functions section](#hal-functions) explains this in more detail.
-  - It is your responsibility to clear the mailbox event. You can do this in the event handler.
 - For each core, implement the HAL function that notifies the peer processor about a mailbox event occurrence. This is a part of the HAL, and the section below explains this in more detail.
 - For each core, add the "SPM_MAILBOX" component field for its target node in mbed-os/targets/targets.json file.