fix: Remove deprecated assert (#1528)

This assert checks that there are no cases where the cycles balance of a
canister can be reduced during execution. However, since this assert
[was introduced about 2 years
ago](1d4692f),
new legitimate cases have been added, like when the storage reservation
mechanism kicks in or the canister calls `cycles_burn` API, that can
reduce the canister's cycle balance. The assert is therefore deprecated
and should be removed.

It replicates the
[change](5d1beac)
that has already been patched on all IC subnets as part of the security
hotfix that was performed over the last couple of days.

rs/execution_environment/src/execution/response.rs

@@ -452,12 +452,6 @@ impl ResponseHelper {
                 round.counters.charging_from_balance_error,
             );
 
-        if let Some(state_changes) = &canister_state_changes {
-            let requested = state_changes.system_state_changes.removed_cycles();
-            // A cleanup callback cannot accept and send cycles.
-            assert_eq!(requested.get(), 0);
-        }
-
         apply_canister_state_changes(
             canister_state_changes,
             self.canister.execution_state.as_mut().unwrap(),