zephyr: Remove scratch from flash_area_id_from_multi_image_slot #11

Job	Run time
environment (esp32, secureboot-sign-rsa2048,secureboot-sign-rsa3072,secureboot-sign-ec256,secureb...	1m 56s
environment (esp32, serialrecovery)	1m 23s
environment (esp32s2, secureboot-sign-rsa2048,secureboot-sign-rsa3072,secureboot-sign-ec256,secur...	1m 43s
environment (esp32s2, serialrecovery)	1m 19s
environment (esp32s3, secureboot-sign-rsa2048,secureboot-sign-rsa3072,secureboot-sign-ec256,secur...	2m 6s
environment (esp32s3, serialrecovery)	1m 32s
environment (esp32c3, secureboot-sign-rsa2048,secureboot-sign-rsa3072,secureboot-sign-ec256,secur...	1m 40s
environment (esp32c3, serialrecovery)	1m 22s
environment (esp32, multi-image,multi-boot, multi)	1m 43s
environment (esp32s3, multi-image,multi-boot, multi)	1m 28s
	16m 12s

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