zephyr: boards: Remove CONFIG_FPROTECT from nrf54l15 #1847

Job	Run time
config (RELEASE 2,4,6 SIGNATURE)	8m 58s
config (RELEASE 2,4,6 SIGNATURE LOW)	13m 14s
config (RELEASE 2,4,6 SIGNATURE MEDIUM)	17m 15s
config (RELEASE 8,10 SIGNATURE)	6m 37s
config (RELEASE 8,10 SIGNATURE LOW)	9m 14s
config (RELEASE 8,10 SIGNATURE MEDIUM)	11m 51s
config (MINSIZEREL 2,4,6 SIGNATURE)	15m 13s
config (MINSIZEREL 2,4,6 SIGNATURE LOW)	19m 49s
config (MINSIZEREL 2,4,6 SIGNATURE MEDIUM)	23m 45s
config (MINSIZEREL 8,10 SIGNATURE)	10m 28s
config (MINSIZEREL 8,10 SIGNATURE LOW)	13m 45s
config (MINSIZEREL 8,10 SIGNATURE MEDIUM)	16m 22s
	2h 46m 31s

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