apibuild: Simplify uniq function
Use a set (unordered collections of unique elements) [1] to remove
repeated elements in a list.
1: https://docs.python.org/3/tutorial/datastructures.html#sets
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Radostin Stoyanov <rstoyanov1@gmail.com>