boards nrf54l15bsim: Remove uncessary defconfig

This board is using since f4cdb0f
the cracen RNG driver, so there is no need to set default options for
the native_posix entropy driver.

Signed-off-by: Alberto Escolar Piedras <[email protected]>

Author: aescolar

boards/native/nrf_bsim/nrf54l15bsim_nrf54l15_cpuapp_defconfig

@@ -6,5 +6,3 @@ CONFIG_NO_OPTIMIZATIONS=y
 
 # Start SYSCOUNTER on driver init
 CONFIG_NRF_GRTC_START_SYSCOUNTER=y
-
-CONFIG_FAKE_ENTROPY_NATIVE_POSIX_SEED_BY_DEFAULT=n