[#1537] morph: Use (user.ID).ScriptHash() where possible

Pick up changes from TrueCloudLab/frostfs-sdk-go#198.

gopatch:
```
@@
var user expression
@@
-address.StringToUint160(user.EncodeToString())
+user.ScriptHash()
```

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/morph/client/balance/balanceOf.go

@@ -6,13 +6,12 @@ import (
 
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/morph/client"
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/user"
-	"github.com/nspcc-dev/neo-go/pkg/encoding/address"
 )
 
 // BalanceOf receives the amount of funds in the client's account
 // through the Balance contract call, and returns it.
 func (c *Client) BalanceOf(id user.ID) (*big.Int, error) {
-	h, err := address.StringToUint160(id.EncodeToString())
+	h, err := id.ScriptHash()
 	if err != nil {
 		return nil, err
 	}

pkg/morph/client/balance/transfer.go

@@ -6,7 +6,6 @@ import (
 
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/morph/client"
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/user"
-	"github.com/nspcc-dev/neo-go/pkg/encoding/address"
 )
 
 // TransferPrm groups parameters of TransferX method.
@@ -25,12 +24,12 @@ type TransferPrm struct {
 //
 // If TryNotary is provided, calls notary contract.
 func (c *Client) TransferX(ctx context.Context, p TransferPrm) error {
-	from, err := address.StringToUint160(p.From.EncodeToString())
+	from, err := p.From.ScriptHash()
 	if err != nil {
 		return err
 	}
 
-	to, err := address.StringToUint160(p.To.EncodeToString())
+	to, err := p.To.ScriptHash()
 	if err != nil {
 		return err
 	}