remove #defines to prevent use of discouraged external functions

Preventing the use of discouraged or 'insecure' external functions
through defines in an internal header is not a good solution. The
header is not guaranteed to be included universally which makes
overlooking bad use of said functions during review more likely.

There are cases were those functions either are the most straight
forward solution or even have to be used. Using malloc or free is
required if the allocation or release is done by other libraries.
