libC Kconfig: Do not default to picolibc for native_sim due to GETOPT

Defaulting to picolibc when selecting GETOPT is a bit nicer for users
in some cases, but not required.
But too many things require GETOPT (for ex. some SHELL configurations)
in combinations with native posix drivers which do not support
yet embedded libcs (for ex. the native USB driver)
(see https://github.com/zephyrproject-rtos/zephyr/issues/60096

 )

Which leads to configurations in those cases which cannot be built.
Keep defaulting to the external libC in this case.

This reverts the getop part of this commit:
5f8057e2

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>