fix(core): fix RSOD handling in secmon

[cepetr]

This small PR fixes an issue with RSOD in the secure monitor.

The fix removes the transition from handler mode to thread mode inside the system_emergency_rescue() function, which is responsible for cleaning up memory and resources before the RSOD is displayed.

It appears that transitioning from handler mode to thread mode cannot be reliably performed in all circumstances when running in the secure monitor. Since we don't need to invoke error_handler (because we use USE_BOOTARGS_RSOD in the secure monitor), we can safely skip this automatic transition.

[github-actions[bot]]

core UI changes	device test	click test	persistence test
T2T1 Model T	test(screens) main(screens)	test(screens) main(screens)	test(screens) main(screens)
T3B1 Safe 3	test(screens) main(screens)	test(screens) main(screens)	test(screens) main(screens)
T3T1 Safe 5	test(screens) main(screens)	test(screens) main(screens)	test(screens) main(screens)
T3W1	test(screens) main(screens)	test(screens) main(screens)	test(screens) main(screens)
All	main(screens)