update rcutils_get_env to always use getenv (#237)
update rcutils_get_env to always use getenv (#237)

* update rcutils_get_env to use getenv for all platforms

Signed-off-by: Suyash458 <55dbce2e779158d3a96f9b489cd40ec3d03d50fa@gmail.com>
ros2/c_utilities,ros2/c_utilities