* We used several utility functions to parse frostfsid client
subject and extended subject. However, following the changes
in TrueCloudLab/frostfs-contract#97, these utility functions
have become public. So there is no more need to have them here.
* There was a mismatch of slice parameter required length between
frostfs-node's and frostfs-contract's utility functions,
`checkStackItem()` solves this problem.
Signed-off-by: Ekaterina Lebedeva <ekaterina.lebedeva@yadro.com>