modules: tf-m: Bugfix TFM_ISOLATION_LEVEL

TFM_ISOLATION_LEVEL should only be defined in zephyr.
So remove its definition from here.
Fixes NCSDK-26756.

Signed-off-by: Sigurd Hellesvik <sigurd.hellesvik@nordicsemi.no>

modules/trusted-firmware-m/Kconfig.tfm.defconfig

@@ -15,9 +15,6 @@ config TFM_BOARD
 
 if BUILD_WITH_TFM
 
-config TFM_ISOLATION_LEVEL
-	default 1 if SOC_FAMILY_NORDIC_NRF
-
 config TFM_BL2
 	bool
 	default n