tests: disable NRF5 entropy driver on some bsim/qemu tests

CONFIG_ENTROPY_GENERATOR is now enabled by default as soon as
"zephyr,entropy" is set in the device-tree. Since the sub-Kconfig
CONFIG_ENTROPY_NRF5_RNG is also enabled by default on nrf boards,
this means that the driver is pulled in the build and intialized
at boot. This might cause runtime issues during some IRQ/kernel
tests, so it's better to remove "zephyr,entropy" on these tests.

Signed-off-by: Valerio Setti <vsetti@baylibre.com>