util: rename virStorageEncryptionInfoDefFree()

util: rename virStorageEncryptionInfoDefFree()

usually a function call vir*Free() will take a single pointer to an
object as its argument, and will then free all resources associated
with that object, including the object
itself. virStorageEnctyptionInfoDefFree() doesn't do that - it frees
all the subordinate resources of the ojbect, but doesn't free the
object itself; usually a function like that is called
vir*Clear(). Let's rename this function to not be misleading.

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>