Consider unremovable LOCK objects

[alexvanin]

LOCK objects are not stable in NeoFS yet. As for neofs-node v0.28.0-rc.1 they can be removed. However this might be invalid behavior and LOCK objects with expiration header will not be removable by object.Delete request. We need to adopt that as soon as behavior will be changed in NeoFS.

[alexvanin]

LOCK issues in general are blocked by nspcc-dev/neofs-node#1226 and nspcc-dev/neofs-node#1227

[alexvanin]

It seems like we handle unremovable LOCK just fine, according to nspcc-dev/neofs-node#1461 (comment), so we don't have to do any additional work.

To clarify:

• retention compliance should work fine with unremovable NeoFS LOCKs
• retention governance won't allow to remove lock, because NeoFS LOCK objects are unremovable
• legal hold will be possible after Consider legal holds on NeoFS objects neofs-contract#247

[KirillovDenis]

Now we can put one lock in compliance mode and several locks in governance mode (they don't affect each other). Before retention period is end we cannot delete neither lock or object version. After retention period is end object can be successfully deleted.
Everything seems to be ok when this branch to be merged into master.