native_posix is being removed as it has reached its end of life in 4.2,
after being deprecated since 4.0.
Remove the twister support for native_posix[//64] and therefore all
references to them from the testcases and samples yamls, so twister
does not error out.
Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>